Efficient multiplexing of control information in transport block

ABSTRACT

Provided are systems and methods for transmitting data over a wireless channel from a data transmitting node to a data receiving node in a communication system. The data transmitting node comprises second-layer processing circuitry for receiving at least one second-layer SDU, to be mapped onto a resource allocated for data transmission, and for generating a second-layer PDU, including the at least one second-layer SDU and at least one second-layer control element, and first-layer processing circuitry for receiving the second-layer PDU generated by the second-layer processing circuitry and for mapping the second-layer PDU onto the resource allocated for data transmission. The data receiving node comprises first-layer processing circuitry for de-mapping at least one second-layer PDU, and second layer processing circuitry for receiving and parsing the second-layer PDU demapped by the first-layer processing circuitry, the second-layer PDU including at least one second-layer SDU, and at least one second-layer control element.

BACKGROUND 1. Technical Field

The present disclosure relates to transmission and reception processingon multiple layers in a communication system as well as to thecorresponding transmission apparatuses, methods and programs.

2. Description of the Related Art

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving aradio-access technology that is highly competitive. In order to beprepared for further increasing user demands and to be competitiveagainst new radio access technologies, 3GPP introduced a new mobilecommunication system called Long Term Evolution (LTE). LTE is designedto meet the carrier needs for high speed data and media transport aswell as high capacity voice support through to the next decade. Theability to provide high bit rates is a key measure for LTE. The workitem (WI) specification on Long-Term Evolution (LTE) called Evolved UMTSTerrestrial Radio Access (UTRA) and UMTS Terrestrial Radio AccessNetwork (UTRAN) is finalized as Release 8 (Rel. 8 LTE). The LTE systemrepresents efficient packet based radio access and radio access networksthat provide full IP-based functionalities with low latency and lowcost. In LTE, scalable multiple transmission bandwidths are specifiedsuch as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieveflexible system deployment using a given spectrum. In the downlink,Orthogonal Frequency Division Multiplexing (OFDM) based radio access wasadopted because of its inherent immunity to multipath interference (MPI)due to a low symbol rate, the use of a cyclic prefix (CP), and itsaffinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA) based radioaccess was adopted in the uplink, since the provision of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmission power of the user equipment(UE). Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniques,and a highly efficient control signaling structure is achieved in Rel. 8LTE.

LTE Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2 . TheE-UTRAN consists of eNBs, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe UE. The eNB hosts the Physical (PHY), Medium Access Control (MAC),Radio Link Control (RLC), and Packet data Control Protocol (PDCP) layersthat include the functionality of user-plane header-compression andencryption. It also offers Radio Resource Control (RRC) functionalitycorresponding to the control plane. It performs many functions includingradio resource management, admission control, scheduling, enforcement ofnegotiated UL QoS, cell information broadcast, ciphering/deciphering ofuser and control plane data, and compression/decompression of DL/UL userplane packet headers. The eNBs are interconnected with each other bymeans of the X2 interface. The eNBs are also connected by means of theS1 interface to the EPC (Evolved Packet Core), more specifically to theMME (Mobility Management Entity) by means of the S1-MME and to theServing Gateway (S-GW) by means of the S1-U. The S1 interface supports amany-to-many relation between MMEs/Serving Gateways and eNBs. The SGWroutes and forwards user data packets, while also acting as the mobilityanchor for the user plane during inter-eNB handovers and as the anchorfor mobility between LTE and other 3GPP technologies (terminating S4interface and relaying the traffic between 2G/3G systems and PDN GW).For idle state UEs, the SGW terminates the DL data path and triggerspaging when DL data arrives for the UE. It manages and stores UEcontexts, e.g. parameters of the IP bearer service, network internalrouting information. It also performs replication of the user traffic incase of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode UE tracking and paging procedures includingretransmissions. It is involved in the bearer activation/deactivationprocess and is also responsible for choosing the SGW for a UE at theinitial attach and at time of intra-LTE handover involving Core Network(CN) node relocation. It is also responsible for authenticating the user(by interacting with the HSS). The Non-Access Stratum (NAS) signalingterminates at the MME and it is also responsible for generation andallocation of temporary identities to UEs. It checks the authorizationof the UE to camp on the service provider's Public Land Mobile Network(PLMN) and enforces UE roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roamingUEs.

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots, wherein the first downlink slotcomprises the control channel region (PDCCH region) within the firstOFDM symbols. Each subframe consists of a give number of OFDM symbols inthe time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), whereineach OFDM symbol spans over the entire bandwidth of the componentcarrier. The OFDM symbols thus each consists of a number of modulationsymbols transmitted on respective subcarriers.

Assuming a multi-carrier communication system, e.g. employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block (PRB) is defined as consecutive OFDM symbolsin the time domain (e.g. 7 OFDM symbols) and consecutive subcarriers inthe frequency domain (e.g. 12 subcarriers for a component carrier). In3GPP LTE (Release 8), a physical resource block thus consists ofresource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (for further details on the downlinkresource grid, see for example 3GPP TS 36.211, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, section 6.2, available at http://www.3gpp.org).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair”, or equivalent “RB pair” or “PRBpair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources. Similar assumptions for the component carrierstructure apply to later releases too.

General Overview of the OSI Layer

FIG. 3A provides a brief overview of a layer model on which the furtherdiscussion of the LTE architecture is based.

The Open Systems Interconnection Reference Model (OSI Model or OSIReference Model) is a layered abstract description for communication andcomputer network protocol design. The OSI model divides the functions ofa system into a series of layers. Each layer has the property of onlyusing the functions of the layer below, and only exporting functionalityto the layer above. A system that implements protocol behaviorconsisting of a series of these layers is known as a ‘protocol stack’ or‘stack’. Its main feature is in the junction between layers whichdictates the specifications on how one layer interacts with another.This means that a layer written by one manufacturer can operate with alayer from another. For the purposes of the present disclosure, only thefirst three layers will be described in more detail below.

The physical layer or layer 1's main purpose is the transfer ofinformation (bits) over a specific physical medium (e.g. coaxial cables,twisted pairs, optical fibers, air interface, etc.). It converts ormodulates data into signals (or symbols) that are transmitted over acommunication channel.

The purpose of the data link layer (or Layer 2) is to shape theinformation flow in a way compatible with the specific physical layer bybreaking up the input data into data frames (Segmentation AndRe-assembly (SAR) functions). Furthermore, it may detect and correctpotential transmission errors by requesting a retransmission of a lostframe. It typically provides an addressing mechanism and may offer flowcontrol algorithms in order to align the data rate with the receivercapacity. If a shared medium is concurrently used by multipletransmitters and receivers, the data link layer typically offersmechanisms to regulate and control access to the physical medium.

As there are numerous functions offered by the data link layer, the datalink layer is often subdivided into sublayers (e.g. RLC and MAC layersin UMTS). Typical examples of Layer 2 protocols are PPP/HDLC, ATM, framerelay for fixed line networks and RLC, LLC or MAC for wireless systems.More detailed information on the sublayers PDCP, RLC and MAC of layer 2is given later. It is noted that in the present application thesublayers are also referred to as “layer” and thus the term “layer”employed herein does not necessarily mean a layer of the OSI model.

The network layer or Layer 3 provides the functional and proceduralmeans for transferring variable length packets from a source to adestination via one or more networks while maintaining the quality ofservice requested by the transport layer. Typically, the network layer'smain purposes are inter alia to perform network routing, networkfragmentation and congestion control functions. The main examples ofnetwork layer protocols are the IP Internet Protocol or X.25.

With respect to Layers 4 to 7, it should be noted that depending on theapplication and service it is sometimes difficult to attribute anapplication or service to a specific layer of the OSI model sinceapplications and services operating above Layer 3 often implement avariety of functions that are to be attributed to different layers ofthe OSI model. Therefore, especially in TCP(UDP)/IP based networks,Layer 4 and above is sometimes combined and forms a so-called“application layer”.

Layer Services and Data Exchange

In the following, the terms service data unit (SDU) and protocol dataunit (PDU) as used herein are defined in connection with FIG. 3B. Inorder to formally describe in a generic way the exchange of packetsbetween layers in the OSI model, SDU and PDU entities have beenintroduced. An SDU is a unit of information (data/information block)transmitted from a protocol at layer N+1 that requests a service from aprotocol located at layer N via a so-called service access point (SAP).A PDU is a unit of information exchanged between peer processes at thetransmitter and at the receiver of the same protocol located at the samelayer N.

A PDU is generally formed by a payload part consisting of the processedversion of the received SDU(s) preceded by a layer N specific header andoptionally terminated by a trailer. Since there is no direct physicalconnection (except for Layer 1) between these peer processes, a PDU isforwarded to the layer N−1 for processing. Therefore, a layer N PDU is,from a layer N−1 point of view, an SDU.

LTE User Plane (U-Plane, UP) and Control Plane (C-Plane, CP) Protocols:

The LTE layer 2 user-plane/control-plane protocol stack comprises threesublayers PDCP, RLC and MAC.

As explained before, at the transmitting side, each layer receives a SDUfrom a higher layer for which the layer provides a service and outputs aPDU to the layer below. The RLC layer receives packets from the PDCPlayer. These packets are called PDCP PDUs from a PDCP point of view andrepresent RLC SDUs from an RLC point of view. The RLC layer createspackets which are provided to the layer below, i.e. the MAC layer. Thepackets provided by RLC to the MAC layer are RLC PDUs from an RLC pointof view and MAC SDUs from a MAC point of view. At the receiving side,the process is reversed, with each layer passing SDUs up to the layerabove, where they are received as PDUs.

While the physical layer essentially provides a bitpipe, protected byturbo-coding and a cyclic redundancy check (CRC), the link-layerprotocols enhance the service to upper layers by increased reliability,security and integrity. In addition, the link layer is responsible forthe multi-user medium access and scheduling. One of the main challengesfor the LTE link-layer design is to provide the required reliabilitylevels and delays for Internet Protocol (IP) data flows with their widerange of different services and data rates. In particular, the protocolover-head must scale. For example, it is widely assumed that voice overIP (VoIP) flows can tolerate delays on the order of 100 ms and packetlosses of up to 1 percent. On the other hand, it is well-known that TCPfile downloads perform better over links with low bandwidth-delayproducts. Consequently, downloads at very high data rates (e.g., 100Mb/s) require even lower delays and, in addition, are more sensitive toIP packet losses than VoIP traffic.

Overall, this is achieved by the three sublayers of the LTE link layerthat are partly intertwined. The Packet Data Convergence Protocol (PDCP)sublayer is responsible mainly for IP header compression and ciphering.In addition, it supports lossless mobility in case of inter-eNBhandovers and provides integrity protection to higher layer-controlprotocols. The radio link control (RLC) sublayer comprises mainly ARQfunctionality and supports data segmentation and concatenation. Thelatter two minimize the protocol overhead independent of the data rate.Finally, the medium access control (MAC) sublayer provides HARQ and isresponsible for the functionality that is required for medium access,such as scheduling operation and random access.

In particular, The Medium Access Control (MAC) layer is the lowestsublayer in the Layer 2 architecture of the LTE radio protocol stack andis defined by e.g. the 3GPP technical standard TS 36.321, currentversion 13.0.0. The connection to the physical layer below is throughtransport channels, and the connection to the RLC layer above is throughlogical channels. The MAC layer therefore performs multiplexing anddemultiplexing between logical channels and transport channels: the MAClayer in the transmitting side constructs MAC PDUs, known as transportblocks, from MAC SDUs received through logical channels, and the MAClayer in the receiving side recovers MAC SDUs from MAC PDUs receivedthrough transport channels.

The MAC layer provides a data transfer service (see sub-clauses 5.4 and5.3 of TS 36.321) for the RLC layer through logical channels, which areeither control logical channels which carry control data (e.g. RRCsignaling) or traffic logical channels which carry user plane data. Onthe other hand, the data from the MAC layer is exchanged with thephysical layer through transport channels, which are classified asdownlink or uplink. Data is multiplexed into transport channelsdepending on how it is transmitted over the air. In addition to the MACSDUs, the MAC PDUs may further comprise MAC control elements of severaltypes and padding, if necessary.

The Physical layer is responsible for the actual transmission of dataand control information via the air interface, i.e. the Physical Layercarries all information from the MAC transport channels over the airinterface on the transmission side. Some of the important functionsperformed by the Physical layer include coding and modulation, linkadaptation (AMC), power control, cell search (for initialsynchronization and handover purposes) and other measurements (insidethe LTE system and between systems) for the RRC layer. The Physicallayer performs transmissions based on transmission parameters, such asthe modulation scheme, the coding rate (i.e. the modulation and codingscheme, MCS), the number of physical resource blocks etc. Moreinformation on the functioning of the physical layer can be found in the3GPP technical standard 36.213 current version 13.0.0.

The Radio Resource Control (RRC) layer controls communication between aUE and an eNB at the radio interface and the mobility of a UE movingacross several cells. The RRC protocol also supports the transfer of NASinformation. For UEs in RRC_IDLE, RRC supports notification from thenetwork of incoming calls. RRC connection control covers all proceduresrelated to the establishment, modification and release of an RRCconnection, including paging, measurement configuration and reporting,radio resource configuration, initial security activation, andestablishment of Signaling Radio Bearer (SRBs) and of radio bearerscarrying user data (Data Radio Bearers, DRBs).

The radio link control (RLC) sublayer comprises mainly ARQ functionalityand supports data segmentation and concatenation, i.e. RLC layerperforms framing of RLC SDUs to put them into the size indicated by theMAC layer. The latter two minimize the protocol overhead independentlyfrom the data rate. The RLC layer is connected to the MAC layer vialogical channels. Each logical channel transports different types oftraffic. The layer above RLC layer is typically the PDCP layer, but insome cases it is the RRC layer, i.e. RRC messages transmitted on thelogical channels BCCH (Broadcast Control Channel), PCCH (Paging ControlChannel) and CCCH (Common Control Channel) do not require securityprotection and thus go directly to the RLC layer, bypassing the PDCPlayer.

RLC Retransmission Protocol

When the RLC is configured to request retransmission of missing PDUs, itis said to be operating in Acknowledged Mode (AM). This is similar tothe corresponding mechanism used in WCDMA/HSPA. Overall, there are threeoperational modes for RLC: Transparent Mode (TM), Unacknowledged Mode(UM), and Acknowledged Mode (AM). Each RLC entity is configured by RRCto operate in one of these modes.

In Transparent Mode no protocol overhead is added to RLC SDUs receivedfrom higher layer. In special cases, transmission with limitedsegmentation/reassembly capability can be accomplished. It has to benegotiated in the radio bearer setup procedure, whethersegmentation/reassembly is used. The transparent mode is e.g. used forvery delay-sensitive services like speech.

In Unacknowledged Mode data delivery is not guaranteed since noretransmission protocol is used. The PDU structure includes sequencenumbers for integrity observations in higher layers. Based on the RLCsequence number, the receiving UM RLC entity can perform reordering ofthe received RLC PDUs. Segmentation and concatenation are provided bymeans of header fields added to the data. The RLC entity inUnacknowledged mode is unidirectional, since there are no associationsdefined between uplink and downlink. If erroneous data is received, thecorresponding PDUs are discarded or marked depending on theconfiguration. In the transmitter, the RLC SDUs which are nottransmitted within a certain time specified by a timer are discarded andremoved from the transmission buffer. The RLC SDUs, received from higherlayer, are segmented/concatenated into RLC PDUs on sender side. Onreceiver side, reassembly is performed correspondingly. Theunacknowledged mode is used for services where error-free delivery is ofless importance compared to short delivery time, for example, forcertain RRC signaling procedures, a cell broadcast service such as MBMSand voice over IP (VoIP).

In Acknowledged Mode the RLC layer supports error correction by means ofan Automatic Repeat Request (ARQ) protocol, and is typically used forIP-based services such as file transfer where error-free data deliveryis of primary interest. RLC retransmissions are for example based on RLCstatus reports, i.e. ACK/NACK, received from the peer RLC receivingentity. The acknowledged mode is designed for a reliable transport ofpacket data through retransmission in the presence of high air-interfacebit error rates. In case of erroneous or lost PDUs, retransmission isconducted by the sender upon reception of an RLC status report from thereceiver.

ARQ is used as a retransmission scheme for retransmission of erroneousor missed PDUs. For instance, by monitoring the incoming sequencenumbers, the receiving RLC entity can identify missing PDUs. Then, anRLC status report can be generated at the receiving RLC side, and fedback to the transmitting RLC entity, requesting retransmission ofmissing or unsuccessfully decoded PDUs. The RLC status report can alsobe polled by the transmitter, i.e. the polling function is used by theRLC transmitter to obtain a status report from RLC receiver so as toinform the RLC transmitter of the reception buffer status. The statusreport provides positive acknowledgements (ACK) or negativeacknowledgment information (NACK) on RLC Data PDUs or portions of them,up to the last RLC Data PDU whose HARQ reordering is complete. The RLCreceiver triggers a status report if a PDU with the polling field set to‘1’ or when an RLC Data PDU is detected as missing. There are certaintriggers defined in sub-clause 5.2.3 of TS 36.322, current version13.0.0, which trigger a poll for an RLC status report in the RLCtransmitter. In the transmitter, transmission is only allowed for thePDUs within the transmission window, and the transmission window is onlyupdated by the RLC status report. Therefore, if the RLC status report isdelayed, the transmission window cannot be advanced and the transmissionmight get stuck. The receiver sends the RLC status report to the senderwhen triggered.

Layer 1/Layer 2 Control Signaling

In order to inform the scheduled users about their allocation status,transport format, and other transmission-related information (e.g. HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length can be amultiple of the subframes. The TTI length may be fixed in a service areafor all users, may be different for different users, or may even bydynamic for each user. Generally, the L1/2 control signaling needs onlybe transmitted once per TTI. Without loss of generality, the followingassumes that a TTI is equivalent to one subframe.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which in most cases includes resource assignments andother control information for a mobile terminal or groups of UEs.Several PDCCHs can be transmitted in one subframe.

Generally, the information sent in the L1/L2 control signaling forassigning uplink or downlink radio resources (particularly LTE(-A)Release 10) can be categorized to the following items:

-   -   User identity, indicating the user that is allocated. This is        typically included in the checksum by masking the CRC with the        user identity;    -   Resource allocation information, indicating the resources (e.g.        Resource Blocks, RBs) on which a user is allocated.        Alternatively, this information is termed resource block        assignment (RBA). Note, that the number of RBs on which a user        is allocated can be dynamic;    -   Carrier indicator, which is used if a control channel        transmitted on a first carrier assigns resources that concern a        second carrier, i.e. resources on a second carrier or resources        related to a second carrier; (cross carrier scheduling);    -   Modulation and coding scheme that determines the employed        modulation scheme and coding rate;    -   HARQ information, such as a new data indicator (NDI) and/or a        redundancy version (RV) that is particularly useful in        retransmissions of data packets or parts thereof;    -   Power control commands to adjust the transmit power of the        assigned uplink data or control information transmission;    -   Reference signal information such as the applied cyclic shift        and/or orthogonal cover code index, which are to be employed for        transmission or reception of reference signals related to the        assignment;    -   Uplink or downlink assignment index that is used to identify an        order of assignments, which is particularly useful in TDD        systems;    -   Hopping information, e.g. an indication whether and how to apply        resource hopping in order to increase the frequency diversity;    -   CSI request, which is used to trigger the transmission of        channel state information in an assigned resource; and    -   Multi-cluster information, which is a flag used to indicate and        control whether the transmission occurs in a single cluster        (contiguous set of RBs) or in multiple clusters (at least two        non-contiguous sets of contiguous RBs). Multi-cluster allocation        has been introduced by 3GPP LTE-(A) Release 10.

It is to be noted that the above listing is non-exhaustive, and not allmentioned information items need to be present in each PDCCHtransmission depending on the DCI format that is used.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in their fields asmentioned above. The different DCI formats that are currently definedfor LTE are as follows and described in detail in 3GPP TS 36.212,“Multiplexing and channel coding”, section 5.3.3.1 (current versionv13.0.0 available at http://www.3gpp.org and). For instance, thefollowing DCI Formats can be used to carry a resource grant for theuplink.

-   -   Format 0: DCI Format 0 is used for the transmission of resource        grants for the PUSCH, using single-antenna port transmissions in        uplink transmission mode 1 or 2.    -   Format 4: DCI format 4 is used for the scheduling of the PUSCH,        using closed-loop spatial multiplexing transmissions in uplink        transmission mode 2.

Uplink Access Scheme for LTE

The uplink scheme allows for both scheduled access, i.e. controlled byeNB, and contention-based access.

In case of scheduled access, the UE is allocated a certain frequencyresource for a certain time (i.e. a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access. Within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e. when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access, the Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines which UE(s) is (are) allowed to transmit, inwhich physical channel resources (frequency), and the correspondingtransport format to be used by the mobile terminal for the transmission.

The allocation information is signaled to the UE via the schedulinggrant, sent on the L1/L2 control channel. The scheduling grant messagecontains information which part of the frequency band the UE is allowedto use, the validity period of the grant, and the transport format theUE has to use for the upcoming uplink transmission. The shortestvalidity period is one sub-frame. Additional information may also beincluded in the grant message, depending on the selected scheme. Only“per UE” grants are used to grant the right to transmit on the UL-SCH(i.e. there are no “per UE per RB” grants). Therefore, the UE needs todistribute the allocated resources among the radio bearers according tosome rules. Unlike in HSUPA, there is no UE based transport formatselection. The eNB decides the transport format based on someinformation, e.g. channel quality feedback, reported schedulinginformation and QoS info, and the UE has to follow the selectedtransport format.

The usual mode of scheduling is dynamic scheduling, by means of downlinkassignment messages for the allocation of downlink transmissionresources and uplink grant messages for the allocation of uplinktransmission resources; these are usually valid for specific singlesubframes. They are transmitted on the PDCCH using the C-RNTI of the UE.Dynamic scheduling is efficient for services types in which the trafficis bursty and dynamic in rate, such as TCP.

In addition to the dynamic scheduling, a persistent scheduling isdefined, which enables radio resources to be semi-statically configuredand allocated to a UE for a longer time period than one subframe, thusavoiding the need for specific downlink assignment messages or uplinkgrant messages over the PDCCH for each subframe. Persistent schedulingis useful for services such as VoIP for which the data packets aresmall, periodic and semi-static in size. Thus, the overhead of the PDCCHis significantly reduced compared to the case of dynamic scheduling.

Logical Channel Prioritization, LCP, Procedure

For the uplink the process by which a UE creates a MAC PDU to transmitusing the allocated radio resources is fully standardized; this isdesigned to ensure that the UE satisfies the QoS of each configuredradio bearer in a way which is optimal and consistent between differentUE implementations. Based on the uplink transmission resource grantmessage signaled on the PDCCH, the UE has to decide on the amount ofdata for each logical channel to be included in the new MAC and, ifnecessary, also to allocate space for a MAC Control Element.

In constructing a MAC PDU with data from multiple logical channels, thesimplest and most intuitive method is the absolute priority-basedmethod, where the MAC PDU space is allocated to logical channels indecreasing order of logical channel priority. This is, data from thehighest priority logical channel are served first in the MAC PDU,followed by data from the next highest priority logical channel,continuing until the MAC PDU space runs out. Although the absolutepriority-based method is quite simple in terms of UE implementation, itsometimes leads to starvation of data from low-priority logicalchannels. Starvation means that the data from the low-priority logicalchannels cannot be transmitted because the data from high-prioritylogical channels take up all the MAC PDU space.

In LTE, a Prioritized Bit Rate (PBR) is defined for each logicalchannel, in order to transmit data in order of importance but also toavoid starvation of data with lower priority. The PBR is the minimumdata rate guaranteed for the logical channel. Even if the logicalchannel has low priority, at least a small amount of MAC PDU space isallocated to guarantee the PBR. Thus, the starvation problem can beavoided by using the PBR.

Constructing a MAC PDU with PBR consists of two rounds. In the firstround, each logical channel is served in decreasing order of logicalchannel priority, but the amount of data from each logical channelincluded in the MAC PDU is initially limited to the amount correspondingto the configured PBR value of the logical channel. After all logicalchannels have been served up to their PBR values, if there is room leftin the MAC PDU, the second round is performed. In the second round, eachlogical channel is served again in decreasing order of priority. Themajor difference for the second round compared to the first round isthat each logical channel of lower priority can be allocated with MACPDU space only if all logical channels of higher priority have no moredata to transmit.

A MAC PDU may include not only the MAC SDUs from each configured logicalchannel but also a MAC CE. Except for a Padding BSR, the MAC CE has ahigher priority than a MAC SDU from the logical channels because itcontrols the operation of the MAC layer. Thus, when a MAC PDU iscomposed, the MAC CE, if it exists, is the first to be included, and theremaining space is used for MAC SDUs from the logical channels. Then, ifadditional space is left and it is large enough to include a BSR, aPadding BSR is triggered and included in the MAC PDU.

The Logical Channel Prioritization is standardized e.g. in 3GPP TS36.321 (version v12.4.0) in sub-clause 5.4.3.1. It is up to the UEimplementation to decide in which MAC PDU a MAC control element isincluded when the UE is requested to transmit multiple MAC PDUs in oneTTI.

Buffer Status Reporting

Buffer status reports (BSR) from the UE to the eNodeB are used to assistthe eNodeB in allocating uplink resources, i.e. uplink scheduling. Forthe downlink case, the eNB scheduler is obviously aware of the amount ofdata to be delivered to each UE; however, for the uplink direction,since scheduling decisions are done at the eNB and the buffer for thedata is in the UE, BSRs have to be sent from the UE to the eNB in orderto indicate the amount of data that needs to be transmitted over theUL-SCH.

Buffer Status Report MAC control elements for LTE consist of either: along BSR (with four buffer size fields corresponding to LCG IDs #0-3) ora short BSR (with one LCG ID field and one corresponding buffer sizefield). The buffer size field indicates the total amount of dataavailable across all logical channels of a logical channel group, and isindicated in number of bytes encoded as an index of different buffersize levels (see also 3GPP TS 36.321 v 12.4.0 Chapter 6.1.3.1).

Which one of either the short or the long BSR is transmitted by the UEdepends on the available transmission resources in a transport block, onhow many groups of logical channels have non-empty buffers and onwhether a specific event is triggered at the UE. The long BSR reportsthe amount of data for four logical channel groups, whereas the shortBSR indicates the amount of data buffered for only the highest logicalchannel group.

The reason for introducing the logical channel group concept is thateven though the UE may have more than four logical channels configured,reporting the buffer status for each individual logical channel wouldcause too much signaling overhead. Therefore, the eNB assigns eachlogical channel to a logical channel group; preferably, logical channelswith same/similar QoS requirements should be allocated within the samelogical channel group.

If the UE has no uplink resources allocated for including a BSR in thetransport block when a BSR is triggered, the UE sends a schedulingrequest (SR) to the eNodeB so as to be allocated with uplink resourcesto transmit the BSR. Either a single-bit scheduling request is sent overthe Physical Uplink Control Channel (PUCCH) (dedicated schedulingrequest, D-SR), or the random access procedure (RACH) is performed torequest an allocation of an uplink radio resource for sending a BSR.

Other MAC Control Elements

MAC Control elements are used for MAC level peer-to-peer signaling.

There are further MAC control elements defined in the LTE. These MACcontrol elements may relate to either uplink or downlink transmission.

Power Headroom Report (PHR) MAC control elements are used by the UE toreport available power Headroom and used then at the base station todetermine how much more uplink bandwidth per subframe a UE is capable ofusing. These elements are provided in the uplink to the scheduling node(eNB) in order to enable it to schedule the uplink transmissionresources to different UEs and avoid that resources are allocated to aUE which is not capable of using them due to its power limitations.Currently, the PHR can only be sent in subframes in which a UE has anuplink transmission grant, i.e. with uplink data transmission.

Activation/Deactivation MAC control elements are used for theactivation/deactivation of SCells, i.e. secondary serving cellsproviding additional resources to the resources of the primary servingcell. To enable reasonable UE battery consumption when carrieraggregation is configured, the activation/deactivation mechanism ofSCells is supported. If the UE is configured with one or more SCells,the eNodeB may activate and deactivate the configured SCells.Activation/Deactivation does not apply to PCell. The MAC CE carries abitmap for the activation and deactivation of SCells: set to 1 denotesactivation of the corresponding SCell, while a bit set to 0 denotesdeactivation. With the bitmap, SCells can be activated and deactivatedindividually, and a single activation/deactivation command canactivate/deactivate a subset of the SCells.

Cell Radio Network Temporary Identifier (C-RNTI) MAC control elementscontrol elements enable the UE to transmit its own C-RNTI during arandom access procedure for the purpose of contention resolution.

UE Contention Resolution Identity MAC Control Elements are used by theeNodeB to transmit the uplink CCCH (Common Control Channel) is due thatthe UE has sent in during the random access procedure for the purpose ofcontention resolution when the UE has no C-RNTI.

DRX command MAC control element is used by the eNodeB to transmit thedownlink PRX command to the UEs.

Timing advance command MAC control element is used by the eNodeB totransmit timing advance command is to the UE's for uplink timingalignment.

MBMS dynamic scheduling information MAC control element is transmittedfor each MCH to inform MBMS-capable UEs about scheduling of datatransmissions on MTCH.

For more information on the MAC control elements listed above, see 3GPPTS 36.321, V13.3.0 section 6.1.3. For each type of MAC control element,one special LCID is allocated.

L1/L2 Processing

FIG. 4 exemplary depicts the data flow of an IP packet through thelink-layer protocols down to the physical layer. The figure shows thateach protocol sublayer adds its own protocol header to the data units aswell as the mapping of the transport block on a subframe. Transportblock (TB) denotes the MAC PDU which is mapped onto the physical layer.

The mapping of the transport block onto the subframe in LTE is performedwithin a so-called transmission time interval (TTI). Generally a singletransport block is mapped in one TTI to one subframe in case of singleinput single output (SISO), i.e. transmitter and receiver operating withone antenna. In case of MIMO/MISO (multiple input multipleoutput/multiple input single output), two codewords corresponding to twotransport blocks may be mapped in one TTI to the physical resources. Ingeneral, more than two transport blocks may be considered for mapping.

The LTE L2 functions are summarized in the following table:

TABLE 1 Table 1: LTE L2 functions (Tx side) UP Protocol layer FunctionsPDCP Bearer mapping (EPS bearer−> radio bearer) Sequence numberingHeader compression Security Routing RLC Sequence numbering SegmentationConcatenation ARQ MAC Scheduling Multiplexing HARQ

In LTE, the RLC layer performs concatenation/segmentation of PDCP PDUs.

When the transmitter knows the transport block (TB) size, the MAC layerperforms logical channel prioritization (LCP) to determine how much dataeach RLC-entity should transmit (provide to the lower layers, i.e. tothe MAC/PHY). Each RLC entity provides one RLC PDU containing one ormore RLC SDUs. For each RLC SDU ending in the RLC PDU, a correspondingL-field (length field) is added, which enables the receiver to extractthe corresponding SDUs. If the last contained RLC SDU does not fitentirely into the RLC PDU, it is segmented, i.e., the remainder of theRLC SDU will be sent in the subsequent RLC PDU(s). Whether the first(last) byte of the RLC PDU corresponds to the first (last) byte of theRLC SDU is indicated by the “Framing Info” flags (2 bit) located in theRLC header. Other than that, segmentation does not any additionaloverhead. In order to re-establish the original order of the data and todetect losses, the RLC sequence number (SN) is added to the RLC PDUheader.

MAC multiplexes the RLC PDUs for different logical channel identifiers(LCIDs) and adds a corresponding subheader with the LCID and theL-field. A high level illustration of the transport block structure isillustrated in FIG. 4 . Recently, the 3GPP has started to study and workon the 5^(th) generation system under the name new radio (NR). NRtargets very high data rates (currently up to 20 Gbit/sec in downlinkand 10 Gbit/sec in uplink).

SUMMARY

As NR is targeting for very high data rates, the processing timeavailable for both transmitter and receiver might be very limitedcompared with the amount of data to be transmitted. One example tominimize transmitter processing time is to minimize the needed real-timeprocessing. For instance, in the LTE, a PDCP PDU can be generated once aPDCP SDU (i.e. an IP packet) is available, i.e. PDCP PDU generation canbe done in a non-real-time manner, i.e. irrespectively of whether or notthere are currently resources granted for the PDCP PDU. However RLC andMAC PDUs can only be generated in real-time manner (i.e. after receptionof the UL grant). Segmentation, concatenation and multiplexing arerequired for DL/UL data SDUs to fit within the total size of assigned TBsize determined by scheduler. Concatenation and segmentation requiresknowledge of the scheduling decision/grant size before it can beperformed so it is subject to strict real time processing requirements.This also implies that the transmitter cannot do any pre-processing foreither the RLC or the MAC layer, e.g., of subheaders/headers before thescheduling/grant information. The inability to perform “pre-processing”incurs a processing delay upon grant reception. If the RLC and to someextent MAC processing could be completed beforehand (the grantreception), then the delay in MAC TB submission to PHY layer would be,comparatively, much smaller.

Furthermore, the MAC PDU format used in LTE does not allow an earlystart of encoding before the TB generation has been finalized. In LTE,MAC PDU is an iterative process since the size of the controlinformation (header) depends e.g. on the number of SDUs in that PDU.This iterative process takes time until the transmission of the MAC PDUmay start. Since MAC control elements (MAC CEs i.e. BSR, PHR) are addedat the beginning of MAC PDU (TB) which needs to be computed beforestarting the transmission of the MAC PDU towards PHY. Computation of BSRcan be only done based on the outcome of LCP whereas the calculation ofPHR depends upon inputting this value to MAC. Hence, pre-computing ofMAC header is not possible and MAC PDU cannot be forwarded to PHY untilthe complete MAC PDU is constructed. Therefore, if MAC control elementsare placed before any MAC SDU, like in LTE, the MAC layer can onlydeliver available MAC SDUs to the PHY after the MAC control elementshave been computed. For example, the computation of a BSR can only bedone after LCP has been completed. Also, power headroom calculation maytake some time and dependent on PHY signals, for example the informationwhether PUCCH is transmitted or not.

One non-limiting and exemplary embodiment provides an approach improvingthe efficiency of the layer processing.

This is achieved by the features of the independent claims.

Advantageous embodiments are subject matter of the dependent claims.

In an embodiment, the techniques disclosed here feature a datatransmitting node that is provided for transmitting data over a wirelesschannel to a data receiving node in a communication system, comprises:second-layer processing circuitry for receiving, from a third layer, atleast one second-layer service data unit, SDU, to be mapped onto aresource allocated for data transmission, and for generating asecond-layer protocol data unit, PDU, including said at least onesecond-layer SDU and at least one second-layer control element, the atleast one second-layer control element placed after any of the at leastone second-layer SDU, first-layer processing circuitry for receiving thesecond-layer PDU generated by the second-layer processing circuitry andmapping the second-layer PDU onto the resource allocated for datatransmission.

Moreover, a computer readable medium is provided for storing thereininstructions, which when executed on a computer, cause the computer toperform the steps of the above methods.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE;

FIG. 3A illustrates the OSI model with the different layers forcommunication;

FIG. 3B illustrates the relationship of a protocol data unit (PDU) and aservice data unit (SDU) as well as the inter-layer exchange of same;

FIG. 4 gives an overview of the different functions in the PDCP, RLC andMAC layers as well as illustrates exemplary the processing of SDUs/PDUsby the various layers;

FIG. 5A is a schematic drawing illustrating processing of data bydifferent layers of the radio access network in LTE user plane;

FIG. 5B is a schematic drawing illustrating pre-processing of MAC-PDUsand their mapping onto physical resources by modifying the preprocessedheaders;

FIG. 6 is a schematic drawing of an exemplary transmission sideprocessing by three layers;

FIG. 7 is a schematic drawing of an exemplary reception side processingby the three layers in case one of two MAC PDUs is lost;

FIG. 8 is a schematic drawing of an exemplary transmission sideprocessing by the three layers in case one of two MAC PDUs is lost;

FIG. 9 is a schematic drawing of an exemplary reception side processingby the three layers in case both MAC PDUs are correctly received;

FIG. 10 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a first transmission;

FIG. 11A is a schematic drawing illustrating a structure of an RLCstatus report;

FIG. 11B is a schematic drawing showing an exemplary structure of astatus report that conveys PDCP sequence number;

FIG. 12 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a first transmission using segment numbers;

FIG. 13 is a schematic drawing showing an exemplary layer processing atthe receiver side for the first transmission using segment numbers;

FIG. 14 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a retransmission using (re)segment numbers;

FIG. 15 is a schematic drawing showing an exemplary layer processing atthe receiver side for the retransmission using (re)segment numbers;

FIG. 16 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a first transmission supportingmulti-connection;

FIG. 17 is a schematic drawing showing an exemplary layer processing atthe receiver side for the first transmission supportingmulti-connection;

FIG. 18 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a retransmission supporting multi-connection;

FIG. 19 is a schematic drawing showing an exemplary layer processing atthe receiver side for the retransmission supporting multi-connection;

FIG. 20 is a block diagram illustrating functional structure ofexemplary data transmitting and data receiving apparatuses;

FIG. 21 is a flow diagram illustrating steps of exemplary methodsperformed at the transmitting and receiving side;

FIG. 22 is a schematic drawing showing an exemplary structure of theuser plane protocol stack for NR;

FIG. 23 is a schematic drawing showing an exemplary MAC PDU format;

FIG. 24 is a schematic drawing of an MAC PDU format including MACcontrol elements following MAC SDUs;

FIG. 25 is a schematic drawing showing another exemplary MAC PDU formatand an exemplary structure of a MAC subheader;

FIG. 26 is a schematic drawing showing an exemplary MAC PDU formatincluding a Buffer Status Report MAC control element;

FIG. 27 is schematic drawing showing an exemplary MAC PDU formatincluding an Activation/Deactivation MAC control element;

FIG. 28 is a schematic drawing showing an exemplary MAC PDU format forprocessing in both directions;

FIG. 29 is a schematic drawing showing the MAC PDU format of FIG. 28 andMAC subheaders including flags which indicate the presence of MACcontrol elements and of further MAC subheaders;

FIG. 30 is a schematic drawing showing yet another exemplary MAC PDUformat;

FIG. 31 is a schematic drawing of a data transmitting node and a datareceiving node;

FIG. 32 is a flow chart illustrating a method for transmitting data anda method for receiving data; and

FIG. 33 is a schematic drawing showing an exemplary PDU format includingMAC control elements at the beginning and at the end.

DETAILED DESCRIPTION

A mobile station or mobile node or user terminal or user equipment (UE)is a physical entity within a communication network. One node may haveseveral functional entities. A functional entity refers to a software orhardware module that implements and/or offers a predetermined set offunctions to other functional entities of a node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The terms “radio resources” as used in the set of claims and in theapplication is to be broadly understood as referring to physical radioresources, such as time-frequency radio resources.

The following exemplary embodiments provide an improved radio interfacelayer processing for the new radio technology envisioned for the 5Gmobile communication systems. As yet, very few details have been agreedon with regard to the 5G mobile communication system, such that manyassumptions have to be made in the following in order to be able toexplain the principles underlying the embodiments. These assumptions arehowever to be understood as merely examples that should not limit thescope of the disclosure. A skilled person will be aware that theprinciples of the present disclosure as laid out in the claims can beapplied to different scenarios and in ways that are not explicitlydescribed herein. For example, the new radio technology will be evolvingfrom the radio technology already defined for LTE(-A), although severalchanges can be expected so as to meet the requirements for 5G mobilecommunication systems. Consequently, particular exemplaryimplementations of the various embodiments could still reuse procedures,messages, functions etc. already defined for the LTE(-A) communicationsystems (according to Release 10/11/12/13/14 etc.) as long as they areequally applicable to both the new radio technology for 5G communicationsystems and to the various implementations as explained for thefollowing embodiments.

According to the present disclosure, the concatenation/segmentationfunctionality is moved from the RLC layer to the MAC entity. Thisapproach provides some advantages, for instance, the RLC PDUs and partlythe MAC PDUs can be pre-constructed at the terminal (if the transmissionis performed in the uplink), before an UL grant is received. Thisreduces processing time through pre-constructing the respective RLC PDUand partly MAC PDU. The RLC layer does not have to wait for MACscheduling decision and the RLC PDU size indication (both carried withresource allocation by L1/L2 signaling). This reduces the processingtime in generating the transport block.

FIG. 5A shows the main functions of protocol layers on the transmitter(TX) and the receiver (RX) sides. As can be seen, at the transmitterside, the segmentation is performed in MAC layer, in cooperation of theRLC layer.

FIG. 5B illustrates basic operation performed on the transmitter side:

a) The RLC and/or MAC PDUs are pre-processed on a per PDCP PDU basis,i.e. the RLC layer does not concatenate the PDCP PDUs. However, the RLClayer may further segment the RLC SDU (PDCP PDU), which is illustratedby two results of a PDCP PDU segmenting, namely R1-PDU1 and R2-PDU2.Pre-processing could be based on a “minimal (or alternatively, anaverage) grant size” which is statistically available, with certain highconfidence level, in a given radio condition (e.g. RSSI/RSRP etc.). So,a pseudo LCP (since it works with estimated grant sizes) is run on thisminimal or an average grant size and the RLC and MAC PDUs arepre-processed accordingly. When the (real) grant is received and the LCPhas been run in the MAC layer, some of the pre-processed RLC PDUs, whichcan be accommodated in the granted resources (i.e. size of thecorresponding MAC PDU is smaller or equal to the grant size for thecorresponding LCID) based on the result of the LCP, will be submitted tothe physical layer. The physical layer may initiate its processing onthese immediately, i.e. in the time instance t1. In FIG. 5B, thepre-segmented R1-PDU1 and R2-PDU1 which have appended the pre-processedMAC header can be accommodated in the granted resources.

b) The pre-segmented R1-PDU2 and R2-PDU2 cannot be accommodated in aswhole to the grated resources and thus, further segmentation of thesePDUs is necessary with the knowledge of the allocation size and afterthe LCP has been performed. In other words, the remaining grant (afterthe above step) would require the pre-processed PDUs to be segmented andtheir corresponding headers need to be recomputed. The segmentation canbe done in the MAC layer (on the RLC PDUs which were alreadypre-processed and submitted to it) or in the RLC layer (RLC re-computingthe header after the segmentation based on result of LCP). After this L2processing, the resulting part(s) (segments) of the MAC PDU aresubmitted to the physical layer. The physical layer may initiate itsprocessing on these subsequently (i.e. at the time instance t2).

In FIG. 5B, the two different RLC entities belong to different logicalchannels. Accordingly, MAC also decides, based on logical channelprioritization procedure (LCP), which of the corresponding MAC PDUs areto be provided to the physical layer at which time point. One example ofa LCP procedure is known from the LTE and referred to above in thebackground section. Nevertheless, the present disclosure is not limitedthereto and in general.

At the receiver side, after physical layer processing, the correspondingreverse steps are performed:

a) The MAC layer performs the de-multiplexing on the basis of the MACheader (basically the LCID field and the Length field) and gives theresulting MAC SDU(s) to the RLC. When the MAC layer passes the MAC SDUto the RLC layer, it also keeps segmentation/concatenation header fieldsince segmentation and concatenation are done by MAC and re-ordering andre-assembly of segments are performed by RLC. This is the reason why MACpasses segmentation header filed to RLC. In other words, the MAC layerpasses it to the RLC not only MAC SDU, but also a part of the MAC headerrelated to segmentation/concatenation.

b) The RLC layer reassembles the RLC PDU segments (if any) beforeforwarding the complete RLC SDU(s) to PDCP. Submission of complete RLCSDUs to PDCP is done also out of order, i.e. including “holes” at theplace where a segment is missing for instance because it has not beencorrectly received within a predefined time or a predefined number ofretransmissions. However, the RLC needs to keep track of the missingPDU(s) and PDU segment(s). The ARQ runs at RLC, so that any missing RLCPDU and/or PDU segment shall be reported to the TX side for a possiblere-transmission. Here, the ARQ shall try to retrieve the missing RLC PDUand/or PDU segment until upon the expiry of a timer, Timer 1. Timer 1 isstarted when a hole first appears (or when the subsequent/next RLC SDUis delivered to the PDCP layer). Upon expiry of Timer 1, RLC shallinform the PDCP layer as well as RRC. The RRC might take further actionslike triggering a Radio Link Failure (RLF) procedure. In general,end-to-end protocols of higher layers like TCP may still take care ofcorrect delivery.

c) The PDCP layer shall decipher the incoming PDUs received from RLC onthe basis of PDCP SN (or COUNT, if available directly from the header;else, it needs to estimate/calculate COUNT from the SN included in thePDCP header). Calculation of COUNT will be done by adjusting the lastCOUNT value with the difference between the last PDCP SN and the PDCP SNvalue in the just received PDCP PDU header. Here, the “last” refers tothe previous PDCP PDU that was successfully deciphered. In addition,PDCP shall wait for the “hole(s)” to arrive from RLC. However, if theindication from RLC (upon Timer 1 expiry) comes before the correspondingPDCP PDU is received, the PDCP SDUs are submitted to the upper layers(including holes).

The above approach is applicable not only to the AM, but also to UM. Inthe case that UM is applied, there are no retransmissions on the RLClayer. Nevertheless, at the receiver side, if a RLC PDU or a RLC PDUsegment is missing, the RLC SDU is still assembled and provided to thePDCP layer.

In the AM, when the RLC Status Report indicates that a RLC PDU and/orPDU segment is missing, the TX side RLC submits the correspondingmissing RLC PDU and/or PDU segment to the MAC layer including a suitableheader to assist the receiver in reassembly of the segment(s) byretransmitting it.

Alternatively, the RLC layer may submit the whole RLC PDU to the MAClayer, even if just a segment of the corresponding RLC PDU was indicatedas missing; in addition, the RLC layer shares the Status Report details(i.e. the entire status report) with the MAC layer. An advantage of thisapproach is to reduce RLC header overhead. If the re-segmentation isdone in the RLC layer, then the RLC layer adds segmentation headerfields which increases header overhead. To overcome this problem, thecomplete RLC PDU is sent to MAC and MAC performs segmentation based theon status report. The status report of RLC is understood by MAC sinceuniversal (common) sequence number is being used between the layers(PDCP, RLC, MAC). In this case, the MAC layer performs there-segmentation based on this knowledge and the result of the LCP, andincludes a suitable header to assist the receiver in reassembly of thesegment(s).

It is noted that the above description refers to the “MAC”, “RLC” and“PDCP”, which are terms employed in the UMTS/LTE(-A) standards. However,the present disclosure is not limited to these standards, or to theiradvancements and may work irrespectively of the used terminology.

In other words, the framework may be seen as a protocol stack in whichthere a first layer responsible for mapping/de-mapping of the dataonto/from the physical resources (corresponding to the physical layer),a second layer (corresponding to MAC) and a third layer (correspondingto RLC and/or PDCP). It is noted that the terms “first layer”, “secondlayer” and “third layer” here do not necessarily correspond to the OSImodel layers.

The reduction of protocol stack processing latency can be achieved in atransmitter side with a first, physical, layer; a second layer; and athird layer in that the second layer receives from the third layerpre-processed third layer PDUs (generated by the third layer withoutknowledge of the resource allocation) and receives (from the receiver inuplink or internally in downlink) resource allocation for the physicallayer. The pre-processed third layer PDUs may be added (already at thethird layer or at the second layer) a header including segmentationinformation. It is noted that such pre-processed third layer PDUs may beprovided for a plurality of third layer entities, corresponding to aplurality of logical channels which may have different priorities.Accordingly, the second layer then may perform a prioritizationprocedure. Based on the received resource allocation and possibly alsobased on the result of prioritization procedure, the second layer thenprovides the first layer with the suitable preprocessed third layer PDUsincluding the segmentation information as the second layer header at afirst time point t1 and possibly performs further segmentation of thepre-processed PDUs and modifies the segmentation information in theheader accordingly before providing the data to the first layer at atime point t2 later than the time point t1.

It is noted that the third layer PDUs received at the second layer maybe already pre-segmented according to ARQ status report if the thirdlayer implements ARQ. But this approach is also applicable if the thirdlayer does not implement ARQ. The pre-segmentation may then be donebased on some statistic measures of past allocations or according toanother rule or does not have to be performed at all.

Moreover, the present disclosure may also be advantageously applied todouble or multi-connectivity. Multi-Connectivity is a mode of operationwhereby a multiple Rx/Tx UE in the connected mode is configured toutilize radio resources amongst E-UTRA and NR provided by multipledistinct schedulers connected via a non-ideal backhaul. In other words,with multiple connectivity a layer above the third layer in thetransmitter (such as a terminal) provides the same packet (IP or PDCP)to be transmitted to multiple base stations (eNBs). The two or more basestations then receive the same packet independently, thus increasing theprobability of correct reception by the network.

The concept of multi-connectivity is somewhat similar to the dualconnectivity which is one promising solution under discussion in 3GPPRAN working groups is the so-called “dual connectivity” concept. Theterm “dual connectivity” is used to refer to an operation where a givenUE consumes radio resources provided by at least two different networknodes connected with non-ideal backhaul. Essentially, a UE is connectedwith both macro cell (macro eNB) and small cell (secondary eNB).Furthermore, each eNB involved in dual connectivity for a UE may assumedifferent roles. Those roles do not necessarily depend on the eNB'spower class and can vary among UEs. However, unlike dual connectivity,where different data are sent from a UE to different eNB s, inmulti-connectivity, the same IP/PDCP packet is transmitted over aplurality of links/cells. Among the multiple receiving eNBs, one isfunctioning as a master eNB, which implements the layer that performsthe reassembly of the segments received via multiple connections. Themaster eNB communicates with the other eNBs.

For instance, speaking in terms of LTE, the PDCP layer takes over thereassembly function in addition to other functions that it is alreadyperforming upon switching from single to multi connectivity. The ARQ maystill run at the RLC layer (in the AM) and in this case the PDCP layerwill need to share the missing (fully or partially) PDCP SN details withthe RLC layer. The PDCP layer will inform the RLC layer about missingpart of segments. Afterwards, the receiving entity of the RLC layer willsend status report to transmitting entity of the RLC layer. Therefore, aseparate ARQ in RLC and PDCP layer is not required, which means singleconnectivity and multi-connectivity, ARQ may both run in RLC layer.Alternatively, the PDCP layer can compose its own Status Report and sendit to the TX-PDCP entity. The Status Report shall contain information onthe missing PDCP PDUs and/or PDU segments.

In order to enable the latency reduction and/or overhead reduction asdescribed above, the present disclosure provides an efficient layermodel to be implemented at the transmitter and the receiver side. Thisincludes one or more of the following:

-   -   Moving the segmentation into the second layer, i.e. as close as        possible to the physical layer which must perform the real-time        processing since it maps the data onto the physical resources        (from the third layer). This provides the possibility of        preparing data for transmission over a shared channel even        before the corresponding grant is received. (The terminal        implementation may make a use of this possibility or not. In        other words, whether or not the terminal timing makes use of        pre-processed PDUs may be left to the implementation).    -   Employing common control information accessed by multiple        layers. Usually, the layer model assumes that each layer only        accesses control information generated on that layer: This leads        sometimes to overlapping duplicated control information being        provided in several layers, i.e. headers of the different        layers' PDU's. This may be the case for the sequence number        which enables reordering of the received data. A common sequence        number may be used for more than one layer (such as PDCP and        RLC) which reduces header overhead.    -   A higher layer (such as third layer or more particular RLC or        PDCP) supports ARQ functionality. Therefore, based on the        third-layer status report, the third layer performs the        segmentation of PDUs. Here it is assumed that the segmentation        of the third layer PDU based on the status report may differ        from the segmentation performed on the basis of the received        allocation performed in the lower layer (second layer or more        particularly MAC). Similar advantage may be achieved if the        third layer provides the second layer with the segmenting        information based on the status report and only the second layer        performs the segmentation based on both the allocation and the        status report. This approach enables saving both time (thanks to        pre-processing) and resources (re-segmentation enables only        retransmitting the missing segments).

Layer 2 Segmentation, Layer 3 Pre-Segmentation for ARQ

In accordance with an embodiment, a data transmitting node is providedfor transmitting data over a wireless interface in a communicationsystem to a data receiving node. In order to implement the functionalityof protocol stack layer model, the data transmitting node comprises athird layer processing unit (hereinafter “a processing unit” can bereplaced as “processing circuitry”) for performing or not an ARQretransmission according to a status report fed back from the datareceiving node and for re-segmenting or not data to be retransmitted (ifany) based on segment length information included in the status report.The re-segmentation includes adding to the segmented data segmentationcontrol information, for instance as a header. This header is alsoadvantageously interpreted and used in a second layer, provided to thesecond layer together with the third layer data unit. In this embodimentit is assumed that the retransmission protocol is handled by the thirdlayer, which does not exclude application of independent ARQ/HARQprotocols in other layers below or above the third layer.

The data transmitting node further comprises a second layer processingunit for receiving, from the third layer processing unit, a third layerdata unit, segmenting the third layer data unit based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isto be applied. The resource allocation may be either received from thedata receiving node or generated at the data transmitting node. Forinstance, if the transmitting node is terminal (UE), the resourceallocation (uplink grant) may be received from a base station, i.e. fromthe data receiving node. On the other hand, if the transmitting node isa base station, the resource allocation for the transmission may begenerated at the base station, and provided to the MAC layer. However,the present disclosure is also applicable to direct communicationbetween terminals or between relays and terminals or relays and basestations.

Finally, the data transmitting node comprises a first layer processingunit for receiving from the second layer one or more of the plurality ofthe second layer data units and mapping the one or more of the pluralityof the second layer data units onto the resources allocated for datatransmission.

It is noted that the data transmitting node may further comprise afourth layer processing unit for providing sequence number within itsheader. The sequence number is increased for each new fourth layer SDU,i.e. with each IP packet, the increasing may be cyclical while thesequence number has a predefined maximum value. The third layeradvantageously does not provide another sequence number but encapsulatesthe fourth layer processing unit including the sequence number providedby the PDCP layer.

In terms of LTE terminology, the first layer may be the physical layer,the second layer may be the MAC layer and the third layer may be the RLClayer, whereas the fourth layer may be the PDCP. However, it is notedthat the third layer may also be considered to be the PDCP layer in someembodiments or one combined layer with functions of both RLC and PDCPespecially in case of architectures evolving based from the present LTE.

FIG. 6 illustrates processing at a transmitter side according to thisembodiment and exemplified using LTE terminology. The transmitter sidemay be the terminal transmitting data in the uplink to a base station.However, the present disclosure is not limited thereto and thetransmitting side may be a terminal transmitting data to anotherterminal or to any other node. Moreover, the present disclosure may alsobe applied to a base station or a relay node or another node being thedata transmitter.

As shown in FIG. 6 , an IP packet 1 with the length of 1200 bytes isprovided to the PDCP layer, thus forming a PDCP SDU. The PDCP SDU isadded a header including a D/C indicator which may be a single bit. Thisbit indicates whether the content of the PDCP PDU is a Data or ControlPDU. In this example, it is set (i.e. the bit is equal to 1) for dataPDU and unset (i.e. the bit is equal to 0) for control PDU. However, ingeneral, the setting/unsetting may be reversed. The PDCP header furtherincludes the PDCP sequence number (SN).

The PDCP PDU1 (with a payload of 1200 bytes) is sent to the RLC layer,thus forming an RLC SDU. The RLC layer includes the relevant RLC headerto the RLC PDU. As can be seen in the figure, the RLC header includesanother D/C flag, a P flag and an RF flag. The D/C flag indicateswhether control or data are carried by the RLC PDU, while the P flag isa polling bit which is set to request a status report from the receiver(peer RLC entity). If it is not set then a status report is notrequested. The RF flag is a re-segmentation flag indicating whether theRLC PDU is a complete PDCP PDU or a PDCP PDU segment. The RF value isinitially set to 0, indicating that the RLC PDU is a complete PDU, andthen delivered to the MAC layer as a part of the RLC PDU1. In thisexample, for the first transmission of data of the PDCP PDU/IP packet,the RLC layer does not perform segmentation; rather the MAC layerperforms the segmentation. Accordingly, for the first transmission, theRF value is always set to 0.

In the example of FIG. 6 , the transmitting MAC entity needs to segmentthe RLC PDU based on the grant received. Further, the grant sizesassumed in this example are 800 and 400 bytes at two differenttransmission occasions (or at least one grant for 800 bytes and the restwaiting for another grant). Thus, the MAC layer segments the RLC PDUcorresponding to a MAC SDU. After the segmentation of the RLC PDU, thetransmitting MAC entity includes segmentation-relevant MAC headerportions into the respective MAC PDUs to indicate segment offset (SO)and last segment field (LSF) of the included RLC PDU and forms the MACPDUs which are referred as MAC PDU1 and MAC PDU2 in FIG. 6 . MAC PDU1contains an 800 byte payload whereas MAC PDU2 contains a 400 bytepayload. MAC PDU1 and MAC PDU2 are sent to TTI0 and TTI1 respectively.The TTI0 and TTI1 are then multiplexed into different resources, forinstance different time resources. However, it is noted that this is notto limit the present disclosure to mapping the two MAC PDUs to differenttime points. More than one MAC PDU may be generally mapped ontodifferent type of resources, for instance different frequencies ordifferent streams of a MIMO system, orthogonal codes, or the like.

The SO field in this example indicates the position of the PDU segmentin bytes within the original PDU. Specifically, the SO field indicatesthe position within the data field of the original PDU to which thefirst byte of the data field of the PDU segment corresponds to. Thefirst byte in the data field of the original PDU is referred by the SOfield value zero. The LSF field indicates whether or not the last byteof the PDU segment corresponds to the last byte of a PDU.

The MAC layer may include into the MAC PDU1 and MAC PDU2 further fieldssuch as logical channel ID (LCID) and an extension flag (E), whichindicates whether or not there are other fields following the MACheader. Value 1 indicates that there is at least one or more E/LCIDfields following this field. Value 0 indicates that there is no moreE/LCID fields following this field implying that the next byte is thestart byte of the MAC SDU. There may some further fields or reservedfields in the header (not shown in the figure).

According to this embodiment also a data receiving node is provided forreceiving data over a wireless interface in a communication system froma data transmitting node. The data receiving node comprises a firstlayer processing unit for de-mapping one or more of a plurality ofsecond layer data units from the resources allocated for datatransmission and for providing the one or more of the plurality of thede-mapped second layer data units to a second layer processing unit.Moreover, the data receiving node further comprises the second layerprocessing unit for performing de-multiplexing of a plurality of thirdlayer unit segments and segmentation control information from the one ormore of the plurality of second layer data units, and forwarding theplurality of the demultiplexed third layer unit segments together withthe segmentation control information to a third layer processing unit.The data receiving node further comprises the third layer processingunit for performing re-ordering of the plurality of the demultiplexedthird layer segments and assembly into a third layer unit.

Thus, the segmentation information which is a part of the second layerdata units (and may be, in particular carried in the second layerheader) is also looked at and used at the third layer. This approachdisregards thus the strict layer separation on one hand; on the otherhand it saves overhead and enables to efficiently perform there-ordering and re-assembly at the third layer. This is particularlyadvantageous if the ARQ procedure is implemented in the third layer,which—however— is not necessary and not limiting for the presentdisclosure.

According to an exemplary implementation, the third layer processingunit in the data receiving apparatus is further configured to generatecontrol data carrying a status report indicating whether or not at leastone third layer unit segment has been received correctly. The statusreport may include at least one of positive acknowledgements or negativeacknowledgements for at least one third layer data unit and/oridentification of correctly received or missing segments of the thirdlayer data unit. Exemplary format of the status report which may beemployed here can be found in 3GPP TS 36.322, Version 13.2.0, Section6.2.1.6 However, it is noted that this is only an example and the statusreport may have a different format and content as long as it enablespositive and/or negative reception acknowledgement for a third layer PDUor its segments.

FIG. 7 illustrates an exemplary reception processing of MAC PDU1 and MACPDU2 received over an error prone channel. As shown in FIG. 7 , MAC PDU1is received (800 bytes payload) correctly but MAC PDU2 (400 bytespayload) is lost (could not been decoded correctly, i.e. the CRCfailed).

The MAC layer performs de-multiplexing of the RLC PDU1 and sends it toRLC layer. The RLC layer then performs reassembling and reordering ofthe MAC segments. The RLC receiving side (RX) sends status reportindicating correct reception of the 800 to 1200 bytes belonging to theMAC PDU1 to the RLC transmitting side (TX). The re-ordering andre-assembling of the RLC PDU segments is performed based on the headerinformation from the MAC layer. This includes in the example of FIG. 7in particular the segment offset and the LSF indicator. The RLC layerD/C field enables distinguishing between the RLC data PDUs and RLCcontrol PDUs such as status reports.

FIG. 8 shows the exemplary subsequent actions at the RLC transmittingside, assuming that the transmitter side is aware of the second missingMAC-PDU2 segment (for instance based on the status report). As shown inFIG. 8 , in this example the RLC TX takes the complete RLC PDU of thecorresponding missing packet from the transmission buffer and performs anew segmentation (re-segmentation) of the 400 (800 to 1200) bytes whichare indicated by the RLC status report as missing. The re-segmentationincludes also attaching the appropriate RLC header. The RLC header hereincludes the segment offset which indicates the position of the RLC PDUsegment which is to be retransmitted by means of an offset in bytes. Inthis example, the segmentation offset SO=801 since the missing 400 bytesfrom 801 to 1200 are to be retransmitted. Then the re-segmented RLC PDUcorresponding to the missing 400 bytes is delivered to the MAC layer.

The MAC layer then performs segmentation of the received RLC PDU andforms MAC PDU1 (which contains 200 bytes of data) and MAC PDU2 (whichalso contains 200 bytes of data), which are then sent to TTI0 and TTI1respectively—as described above with reference to FIG. 6 for the firsttransmission. Of course, in general, the MAC layer only performssegmentation if it is required. Here in this example, the grant size isnot sufficient and that is why the MAC layer forms MAC PDU1 and MACPDU2. If the allocation is sufficient, no segmentation is needed, orpossibly, concatenation is performed (in case the allocation is largerthan needed for one MAC PDU).

In particular, the MAC layer reads the SO field and the LSF field fromthe RLC header and modifies them on the basis of the grant size, i.e. inthis example to reflect the segmentation size of 200 bytes and 200bytes, respectively. As can be seen in FIG. 8 , the MAC layer providesthe new segmentation information in the respective headers of thesegmented MAC PDUs, namely SO=801 and SO=1001, corresponding to theposition of the new segments of data to be retransmitted within thefirst-transmitted (not re-segmented) RLC PDU and the LSF. FIG. 9illustrates an example in which the MAC PDU1 and MAC PDU2 from FIG. 8are both received correctly. The MAC layer delivers the correctlyreceived MAC PDU1 and MAC PDU2 to the RLC layer. The RLC layer performsthe reordering and reassembling of MAC segments and then delivers thecomplete PDCP PDU to the PDCP layer. The reordering is performed basedon the sequence numbers (SN). As mentioned above, a single sequencenumber is advantageously used for both PDCP and RLC layers in order tosave overhead.

In other words, the RLC RX collects all segments of the RLC PDU(retransmitted or correctly received after the first transmission),re-orders them based on the MAC header information and reassembles theRLC PDU. The reassembled PDU may then be provided to the higher layers(such as PDCP or directly IP, if there is no PDCP) for furtherprocessing.

Accordingly, the present disclosure modifies the functions performed bythe different layers of the RAN protocol stack as is illustrated inTable 2 below.

TABLE 2 Table 2: NR protocol stack tasks UP protocol layer FunctionsPDCP TX Header compression SN attached Ciphering Retransmission RLC TXDelivering packets to MAC layer Packet (re)-segmentation onretransmission MAC TX Concatenation/multiplexing Segmentation HARQtransmission MAC RX HARQ reception De-multiplexing RLC RX MAC segmentreordering/status reporting (Retransmission) Packet reassembly Out ofsequence delivery to PDCP PDCP RX Packet deciphering Complete PDU basedreordering/status reporting Header decompression

In the following Tables 3-5 provide examples of the headers of therespective layers PDCP, RLC and MAC.

TABLE 3 Table 3: The description of the PDCP header fields Data/Controlbit D/C indicates whether PDU is data or control PDU (D/C) Sequencenumber 10 bit sequence number (SN)

TABLE 4 Table 4: The description of the RLC header fields Data/ControlD/C indicates whether PDU is data or control PDU bit (D/C)Re-segmentation RF indicates whether PDU is complete or segment flag(RF) PDU. Polling bit (P) The P field indicates whether or not thetransmitting side of an AM RLC entity requests a STATUS report from itspeer.

TABLE 5 Table 5: The description of the MAC header fields Length The LIfield indicates the length in bytes of the indicator corresponding Datafield element present in the MAC (LI) data PDU delivered/received by MACentity. Extension The E field indicates whether this field is the end ofthe bit (E) header or another extension follows or not. Segmentation TheSO field indicates the start position of the first byte offset (SO) ofthe corresponding MAC SDU in bytes. Last segment The LSF is set to 1 toindicate that this is the last field (LSF) segment of the RLC PDU.

In the above tables, the length of the sequence number is exemplified as10 bits. However, it is noted that this is only an example which is notto limit the present disclosure. Already in LTE, the length of the PDCPsequence number can be 5 bit, 7 bits or 12 bits depending on the radiobearer's characteristics. The length of the sequence number is a matterof system design as is clear to those skilled in the art any may beselected to have any length for the purposes of the present disclosure.

As shown in FIG. 6 , the PDCP PDUs are sent to the RLC layer at thereceiver. Advantageously, the PDCP, RLC and MAC layers use a universalsequence number which is understood by all these layers. In thisexample, the PDCP sequence number is used, which is understood by allthree layers, or at least the PDCP and RLC since the SN is notnecessarily needed in the lower layers.

The RLC layer includes the relevant RLC header in the RLC PDU, forinstance the RF field to indicate a complete or segmented PDU. The RFvalue is initially set to 0 and is updated when a status report arrivesat the RLC TX. When the transmitting side transmits the RLC data PDUs,it still stores the RLC PDUs in the retransmission buffer for possibleretransmission. A retransmission may be requested by the receiver bymeans of the status report. As can be seen in FIG. 6 , the RLC PDUs arethen delivered to the MAC layer. Afterwards, the transmitting MAC entityperforms segmentation and/or concatenation on the MAC SDU received fromthe upper layer (RLC) to form the MAC PDU(s).

The size of the MAC PDU at each transmission opportunity (TTI) isdecided and notified by the MAC layer itself depending on the radiochannel conditions and transmission resources available therefor. Asmentioned in the background section, dynamic scheduling may be appliedfor the shared channel so that in each TTI a different allocation ispossible (capable of accommodating different amount of date for instancedue to varying modulation and coding scheme for better link adaptation).

The size of each transmitted MAC PDU can thus be different. Thetransmitting MAC entities include RLC PDUs/MAC SDUs into a MAC PDU inthe order, in which they arrive at the MAC entity. Therefore a singleMAC PDU can contain complete RLC PDUs or an RLC PDU segment since MACmay perform not only segmentation but also concatenation, depending onthe respective segment sizes and allocated resources. If a MAC PDUcontains N (N being an integer larger than 0) RLC PDUs and/or PDUsegments, then the MAC layer shall include N−1 Length fields (L-fields)for all respective corresponding RLC PDUs and/or PDU segments i.e. oneL-field for each RLC PDUs and/or PDU segments except for the last one.

On the receiver side, as shown in FIG. 7 (LI fields are not shown sincethe Example of FIGS. 6-9 relates to segmentation rather thanconcatenation), the MAC layer knows where the actual data starts sinceit knows both the header length, as well as—with the L-field—the MAC PDUlength. The header length is assumed to be known here. For instance, itmay be predefined (for instance specified in a standard) and/orindicated within a field in the header. In the above example, theextension bit is used to indicate whether the header continues orterminates, which makes possible to determine the header size.

The MAC layer performs de-multiplexing of the MAC PDUs without removingthe segmentation fields (SO and LSF) and then the de-multiplexed RLCPDUs/segments are delivered to the RLC layer. When the receiving RLClayer receives the RLC PDU segments, it first reorders and re-assembliesthem if they are received out of sequence (cf. also FIG. 9 ). One of theadvantages of not doing reordering and reassembling in the MAC layer isthe processing time reduction. If one segment is missed in the receiverside, then the MAC layer could not do reassembly and reordering whichwill add delay in delivery to the upper layer (RLC). In order not todelay re-assembling and re-ordering, the MAC layer passes thesegmentation fields (SO, LSF) to the RLC layer since segmentation andconcatenation are performed by the MAC layer, as described above withreference to FIG. 6 . Therefore, the RLC layer reads the segmentationheader field(s) received from the MAC layer and on the basis of thesegmentation (e.g. SO, LSF) and concatenation (e.g. LI) header field(s),the RLC layer performs, where appropriate, the re-ordering andre-assembling. Accordingly, a cross-layer interaction is required inthis example since the receiving RLC layer has to know and use the MAClayer signaling fields.

Any RLC PDUs received out of sequence at the MAC layer are delivered tothe upper layer (RLC). An ARQ operation is performed in the receivingRLC to support an error free transmission (acknowledged mode). In orderto enable the transmitting side to retransmit only the missing RLC PDUs,the receiver side provides an RLC status report to the transmitting sideindicating the missing PDU(s) or PDU segment(s) information for the RLCPDUs.

In response to a status report with one or more PDUs/segments missing,the transmitter of the RLC layer takes the complete RLC PDU of thecorresponding missing packet from the transmission buffer and performs(re)-segmentation on the basis of the missing segment(s) which is/areindicated by the RLC status report. If re-segmentation is performedafter the reception of the status report, the RLC changes the RF fieldfrom 0 to 1. Then the (re)-segmented PDU(s) is/are delivered to the MAClayer, which reads the RF flag. Since the radio conditions maydeteriorate during the retransmission procedure, the missing segment PDUor PDUs may have to be broken up into smaller segmentations(re-segmented) before retransmission (which is done by MAC layer). Thisis illustrated in FIG. 8 , in which the missing 400 byte payload RLC PDUis taken at the RLC layer from the original 1200 byte payload RLC PDU inthe retransmission buffer and further broken (re-segmented) into thesmaller 200 byte payload MAC PDUs.

Re-Segmentation in the MAC Layer

When looking at FIG. 8 , it can be seen that the RLC overhead isslightly increased, since the RLC transmitter performs there-segmentation on the basis of the missing part of the segment, i.e. onthe basis of the 400 bytes long data which was not received correctlyand which is indicated by the RLC status report and then delivered tothe MAC layer. Accordingly, the re-segmentation header (including SO, RFand LSF) is required in the RLC, which increases the RLC headeroverhead.

In order to reduce the overhead, according to an embodiment, there-segmentation is performed in the MAC layer.

In particular, according to this embodiment, a data transmitting node isprovided for transmitting data over a wireless interface in acommunication system to a data receiving node. The data transmittingnode comprises a third layer processing unit for performing an automaticrepeat request, ARQ, retransmission according to a status report fedback from the data receiving node. The data transmitting node furthercomprises a second layer processing unit for receiving, from the thirdlayer processing unit, a third layer data unit, segmenting the thirdlayer data unit according to the status report and based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the segmented third layer data unit. Thefirst layer processing unit is also present for receiving from thesecond layer the plurality of the second layer data units and mappingthe plurality of the second layer data units onto the resourcesallocated for data transmission.

Accordingly, the segmentation functionality is entirely transferred tothe second layer, the closest layer to the physical layer. This isillustrated in FIG. 10 in a greater detail based on a selected example.

The RLC layer of the transmitter adds the PDCP PDU (RLC SDU) a headerincluding the polling bit (if this embodiment is applied with AM ratherthan UM) to request a status report and the D/C field indicating whetherthe RLC PDU carries payload (user) or control data. It is noted that thepresent disclosure is not limited to the RLC layer preforming ARQ sincethe RLC layer may also operate in the unacknowledged mode.

The RLC TX layer delivers the status report received from the RLC RX tothe MAC layer. The MAC layer reads the segmentation information such asthe sequence number (SN), SOstart and SOend value form the status reportand performs the segmentation accordingly. Therefore, the RLC TX takesthe complete RLC PDU from the retransmission buffer and sends it to theMAC TX. This is illustrated in FIG. 10 which shows the RLC PDU includingthe data field with PDCP SDU data of 1200 bytes rather than only the 400bytes as shown in FIG. 8 .

Afterwards, the MAC TX layer performs the segmentation on the basis ofthe segmentation information, e.g. SOstart, SOend and SN which isindicated by the RLC status report and forwarded down to the MAC layerby the RLC layer as shown in FIG. 10 . In accordance therewith, the MACPDU header is generated. The header in FIG. 10 includes the LCID(logical channel identification), the E-bit indicating whether or notfurther header information is present and the segmentation informationincluding here the segment offset (may be in the units of bytes) whichindicates the start of the carried segment within the RLC PDU and thelast segment field (LSF) indicating whether or not the encapsulated RLCPDU segment is the last in the RLC PDU. As can be seen in FIG. 10 , theoffsets of 801 and 1001 doe the two segments of 200 and 200 bytesrespectively are signaled.

FIG. 11A shows a status report (STATUS PDU) as defined in the 3GPP TS36.322, v. 13.2.0. STATUS PDU consists of a STATUS PDU payload and a RLCcontrol PDU header. RLC control PDU header consists of a D/C and a CPTfield. The STATUS PDU payload starts from the first bit following theRLC control PDU header, and it consists of one ACK_SN and one E1, zeroor more sets of a NACK_SN, an E1 and an E2, and possibly a set of aSOstart and a SOend for each NACK_SN. When necessary one to sevenpadding bits are included in the end of the STATUS PDU to achieve octetalignment.

FIG. 11B shows an exemplary format of an RLC status report. Thisexemplary status report is similar and includes similar fields as theLTE status report which is exemplified in FIG. 11A. The status report ofFIG. 11B differs from the LTE status report in FIG. 11A in that the PDCPsequence number is conveyed rather than the RLC sequence number.

In particular, the status report includes a D/C field and a CPT (controlPDU type) field which indicates whether or not the PDU is a status PDU,it indicates the status PDU for the status report. PDCP ACK_SN is a 10bits long field which indicates the SN of the next not received RLC DataPDU which is not reported as missing in the status report (STATUS PDU).The prefix “PDCP” here emphasizes that a common SN is used for the RLCand the PDCP layer which is thus also applied to the status report.

Extension bit 1 (E1) indicates whether or not a set of PDCP NACK_SN, E1and E2 follows; if set to 0—a set of NACK_SN, E1 and E2 does not follow;if set to 1—a set of NACK_SN, E1 and E2 follows.

Negative Acknowledgement SN (NACK_SN), in this example PDCP NACK_SNfield, indicates the SN of the RLC PDU (or portions of it) that has beendetected as lost at the receiving side of the AM RLC entity.

Extension bit 2 (E2) indicates whether or not a set of SOstart and SOendfollows; if set to 0—a set of SOstart and SOend does not follow for thisNACK_SN; if set to 1—a set of SOstart and SOend follows for thisNACK_SN.

According to 36.322, sections 6.2.2.18, 6.2.2.19 describe these SOstartan SOend as follows:

-   -   SOstart (15 bits): The SOstart field (together with the SOend        field) indicates the portion of the RLC PDU with SN=NACK_SN (the        NACK_SN for which the SOstart is related to) that has been        detected as lost at the receiving side of the AM RLC entity.        Specifically, the SOstart field indicates the position of the        first byte of the portion of the RLC PDU in bytes within the        Data field of the RLC PDU    -   SOend (15 bits): The SOend field (together with the SOstart        field) indicates the portion of the RLC PDU with SN=NACK_SN (the        NACK_SN for which the SOend is related to) that has been        detected as lost at the receiving side of the AM RLC entity.        Specifically, the SOend field indicates the position of the last        byte of the portion of the AMD PDU in bytes within the Data        field of the RLC PDU. The special SOend value “111111111111111”        is used to indicate that the missing portion of the AMD PDU        includes all bytes to the last byte of the AMD PDU. In other        words, the SOstart and SOend indicate respectively the start and        the end of the negatively acknowledged RLC PDU segments.

Segment Number

The segment offsets (start and end together) which are typically 30 bitslong which increases MAC sub-header overhead, especially for smallersegments.

In order to reduce the overhead, in this embodiment, the segmentidentification is thus a segment number indicating a sequence number ofthe segment of the third layer data unit within the third layer dataunit. This segment number may be used in the data PDUs as illustrated inthe drawing, i.e. instead of the SO field. However, the segment numbermay also be advantageously used in the status report (STATUS PDU) toreplace the SOstart and SOend.

In one example, the MAC sub-header (i.e. portion of the header relatedto segmentation) is reduced by using a 4 bit long segment number insteadof the 30 bit segment offsets (15 bits of SOstart and 15 bits SOend).Thus, the MAC layer performs segmentation on the basis of the 4 bitsindicating the segment number. The 4 bit segment number allowsdistinguishing a maximum of 16 segments. However the number 4 is onlyfor exemplary purposes here. If more or less segments are necessary forthe corresponding user plane layer architecture, this could be doneusing a higher number of bits. The approach of this embodiment is toreduce the overhead by signaling a segment number for each segmentinstead of the start and end of each segment within the RLC PDU. Sincethe number of segments is certainly smaller than the number of bits inthe RLC PDU to which the offsets are related, overhead is generallysaved by addressing the segments rather than the offset.

The employing of the segment number is illustrated in FIG. 12 for thetransmission side. In particular, FIG. 12 shows an IP packet provided tothe PDCP layer, where it is added a D/C field and the PDCP SN andprovided together with this header information to the RLC layer. The RLClayer encapsulates the PDCP PDU by adding thereto an own headerincluding the D/C field and the polling field. Here, RF field is notnecessary as the segmentation is not performed at the RLC layer. Rather,the RLC PDU1 is provided whole to the MAC layer.

As shown in FIG. 12 , in the MAC layer, the RLC PDU is divided into twosegments: segment 0 and segment 1 which containing 800 and 400 bytes,respectively. This segmentation may be performed based on the allocationsize. After the segmentation of the RLC PDU, the transmitting MAC entityincludes the relevant MAC headers to form the MAC PDU. In particular,the header includes a Length Indicator (LI) indicating the length of thesegment, the segment number (e.g. the above described 4 bits), the LastSegment Field (LSF) and a field R set to 0 (which indicates that there-segmentation does not follow) for the included RLC PDU. The LI fieldis needed in case of concatenation where one MAC PDU contains 2 or moreRLC PDUs. In case of segmentation, the grant size is known, so thatreceiver knows the size of grant and can perform the reverse operationaccordingly.

The MAC layer then forms, based on the segmentation information the twoMAC PDUs which are referred as MAC PDU1 and MAC PDU2 in FIG. 12 . MACPDU1 and MAC PDU2 are sent to the respective transmission time intervalsTTI0 and TTI1 respectively.

TABLE 6 Table 6: MAC header fields Length The LI field indicates thelength in bytes of the indicator corresponding Data field elementpresent in the MAC data (LI) PDU delivered/received by MAC entity. E.g.in FIG. 12, the LI of the MAC PDU1 indicates 800 and the LI of the MACPDU2 indicates 400. Extension The E field indicates whether this fieldis the end of the bit (E) header or another extension follows or not.E.g. in FIG. 12, the E field is set since further fields are present inboth MAC PDU1 and MAC PDU2. R The R field indicates whetherre-segmentation follows or not R value is initially set to 0. E.g. inFIG. 12, the R = 0 since the respective MAC PDU1 and MAC PDU2 are notfurther segmented. Last The LSF is set to 1 to indicate that this is thelast segment segment of the RLC PDU. field E.g. in FIG. 12, for MAC PDU,1 the LSF = 0 since MAC (LSF) PDU1 is not the last RLC PDU segment andfor MAC PDU2, the LSF = 1 since MAC PDU2 is the last segment of the RLCPDU. Last Re- The LRF is set to 1 to indicate that this is the last re-segment segment of the RLC PDU. field E.g. in FIG. 12, this field is notpresent since the R field was (LRF) not set. Segment The segment isassigned segment number 0 to 15. number E.g. in FIG. 12, for MAC PDU1which is the first RLC PDU segment the segment number has a value of 0(0000 in binary notation assuming the length of this field being 4 bits)and for MAC PDU2 which is the second and last RLC PDU segment thesegment number has a value of 1 (0001 in the binary notation)

FIG. 13 illustrates an exemplary receiver side layer processing for thisembodiment in which the segment numbers are employed instead of thesegment offsets.

As shown in FIG. 13 , on the receiver side, MAC PDU1 is receivedcorrectly while MAC PDU2 is lost. The MAC layer delivers MAC PDU1together with the segmentation header (including R, segment number andLSF) to the RLC layer, whereas the RLC layer of the receiving side sendsa status report indicating the missing 800 to 1200 bytes (i.e. MAC PDU2)to the transmitting RLC entity. The RLC layer performs then there-assembly and re-ordering of the RLC segments. Here, only the first800 byte segment is correctly received and thus no reordering has to beperformed in this example.

FIG. 14 shows an exemplary transmitter side layer processing uponreceiving the status report from the data receiving side. As shown inFIG. 14 , the RLC layer takes the complete RLC PDU from theretransmission buffer (this is illustrated by the PDCP SDU data of 1200bytes included in the RLC PDU rather than only the missing 400 bytes).The MAC layer performs then a re-segmentation on the basis of the RLCstatus report.

After the re-segmentation of RLC PDU, the transmitting MAC entityincludes the relevant MAC headers in the respective re-segmented MACPDUs to indicate their length (LI), a 3 bits re-segment number, lastre-segment field (LRF) and R=1 (which indicates that a re-segmentationfollows) for the respective included RLC PDUs and forms the MAC PDUswhich are referred as MAC PDU1 and MAC PDU2 in FIG. 14 .

If required, the MAC layer may perform re-segmentation of the missingpart of segment number e.g. when the missing segment, as reported in RLCStatus report, cannot fit in the available grant for the correspondingLCID (after running LCP). For this purpose, MAC may use e.g. 3 bits (ormore, if required) to identify “re-segments” of the correspondingsegment of an RLC PDU.

In summary, the second layer processing unit includes into the header ofthe second layer data unit the segment identification comprising are-segment number indicating a sequence number of the segment of thethird layer data unit within the segment of the third layer data unit,the re-segment number being signaled using less bits than the segmentnumber. However, it is noted that this is not to limit the presentdisclosure. The size of the segment number and re-segment number mayalso be the same. Another term, which may be employed for “re-segment”is a “sub-segment” since it is a sub-segment of a segment resulting fromprevious segmentation.

In FIG. 14 , alternatively, the segment number may be used for thesegments and the segment offset may be used for the sub-segments insteadof the sub-segment number, since it is assumed that retransmissions arenot as frequent and thus higher overhead may be acceptable.

FIG. 15 shows the receiving side layer processing upon receiving theretransmission of the MAC PDU1 and MAC PDU2 shown in FIG. 14 .

As shown in FIG. 15 , the MAC layer performs de-multiplexing of MAC PDU1and MAC PDU2 and removes part of their header. However, the MAC layerkeeps the relevant segmentation header fields (R field, segment number,LSF, LRF and re-segment number) since the re-ordering and re-assemblingis performed in the RLC layer. The RLC performs then the re-ordering andre-assembling of the MAC segments and sends the result (PDCP PDU) to thePDCP layer.

Reordering and Reassembly at the Second Layer

According to another embodiment of the present disclosure, the receivingside is further modified. In particular, instead of performing there-ordering and the re-assembly in the RLC layer, the MAC layer performsre-ordering and re-assembly. In that case, cross-layer interaction isnot required. In this configuration, the MAC layer is also responsiblefor performing the retransmission processing. If any parts of thesegments are missed, then the receiving entity of MAC layer sends thestatus report to the MAC TX. The MAC status report will slightly differfrom the RLC status report. In particular, the LCID field will beprovided in the status report to differentiate which status reportbelongs to which LCID (logical channel).

In other words, a data receiving node for receiving data over a wirelessinterface in a communication system from a data transmitting node,comprising: a first layer processing unit for de-mapping one or more ofa plurality of second layer data units from the resources allocated fordata transmission and for providing the one or more of the plurality ofthe de-mapped second layer data units to a second layer processing unit;the second layer processing unit for performing de-multiplexing of aplurality of third layer unit segments and segmentation controlinformation from the one or more of the plurality of second layer dataunits, and forwarding the plurality of the demultiplexed third layerunit segments together with the segmentation control information to athird layer processing unit; Moreover, the second layer processing unitis also performing re-ordering of the plurality of the demultiplexedthird layer unit segments and assembly of the demultiplexed third layerunit segments into a third layer data unit. The second layer processingunit may also be configured to check whether or not the data arereceived correctly and send a status report to the peer second layerentity. This embodiment of the receiver is particularly suitable for thereceiver embodiment with the segmentation/concatenation performed in thesecond layer described above.

Multi-Connectivity/Dual Connectivity for More eNBs Same Bearer to MoreLinks.

In case of multi-connectivity, the PDCP layer distributes duplicatepackets into different eNB.

The following Table 7 describes protocol stack of multi-connectivitywith the main functions of each layer.

TABLE 7 Table 7: Functions of protocol layers supportingmulti-connectivity Functions PDCP TX Header compression SN attachingCiphering Packet segmentation on retransmission RLC TX MAC TXConcatenation/multiplexing Segmentation HARQ transmission MAC RX HARQreception De-multiplexing RLC RX PDCP RX Packet deciphering Segmentbased reordering/reassembly/status reporting Complete PDU basedreordering/status reporting Header decompression

FIG. 16 illustrates transmitting side layer processing for a case of anew transmission of an IP packet 1 in accordance with this embodimentsupporting multi-connectivity.

In particular, the first layer is a physical layer, the second layer isa Medium Access Control, MAC, layer and the third layer is a Packet DataControl Protocol, PDCP, layer. However, it is noted that PDCP and RLClayer may also be combine into one layer, or RLC may perform thefunctionality. The third layer processing unit is configured to providethe same third layer data unit to different lower layer stacks fortransmission, over the wireless interface, to different respective basestations, or, in general data receiving nodes. The lower layer stacksare capable of performing segmentation/reassembly individually andindependently from each other. The lower layer stack may includephysical layer and MAC. However, it may also still include RLC layer.

As also noted above, the layer may be also called differently and havedifferent functions than the current LTE layers. In general, themulti-connectivity has a one layer in common which receives a packerfrom higher layers and provides multiple (more than one) copies of thepacket encapsulated as own PDU to the lower layers of respectivemultiple stacks. The multiple stacks handle segmentation and reassemblyas described in any of the above embodiments and separately andindependently from each other, which ensures that they can adapt totheir respective physical channel conditions and status of datareception.

The third layer advantageously controls the retransmission processing.In the above multi-connectivity scenario it is not necessary that eachlower layer stack at the receiver side receives and reassembles thepacket correctly. It is enough when one of them which collects segmentsof the packets from all other stacks is capable of reassemble thepacket. This provides a kind of diversity and increases the throughput.

As shown in FIG. 16 , IP packet 1 is attached to the PDCP header on thePDCP layer and the corresponding PDCP PDU is sent to two different basestations, here eNB1 and eNB2. The base stations eNB1 and eNB2 (networknodes) implement respectively protocol layers as described above(RLC/MAC/PHY). The eNB1 passes the PDCP PDU which corresponds to the RLCPDU1 into two segments MAC PDU1 and MAC PDU2 containing 800 byte and 400bytes respectively. The eNB2 may employ a different segmentation sincethe channel quality in different cells may differ. Thus in this example,eNB2 segments the RLC PDU1 into two segments MAC PDU1 and MAC PDU2containing 500 byte and 700 bytes respectively. The RLC layer, ifworking in acknowledged mode, may be further responsible for ARQfunctionality. However, as described above, the PDCP may control the RLCretransmissions. In particular, each RLC layer (of the respective eNB)may pass the status reports to the PDCP of the master eNB, which decideswhether or not a retransmission is necessary and for which segment ofthe packet. The PDCP then instructs the respective RLC layers to performthe retransmissions accordingly.

FIG. 17 illustrates processing at the receiving side. As shown in FIG.17 , eNB1 receives MAC PDU1 which contains 0 to 800 bytes whereas theMAC PDU2 with 801 to 1200 bytes is lost. On the other hand, eNB2receives MAC PDU1 containing 0 to 500 bytes whereas 501 to 1200 bytes islost due to missing of MAC PDU2. The PDCP layer performs centralre-ordering and re-assembling.

An advantage of not performing the reordering and reassembling in theRLC layer in this embodiment is avoiding unnecessary retransmissionsduring multi-connectivity. If reassembling and reordering were performedin the RLC layer, then the RLC layer of both eNBs will send respectiveindividual RLC status reports to the RLC TX (RLC of eNB1 sends statusreport of 801 to 1200 bytes and RLC of eNB2 sends status report of 501to 1200 bytes, so far actual missing part is 801 to 1200 bytes). In thiscase, RLC TX could retransmit more than the required segments which willbe discarded at RLC RX.

To overcome this problem, the RLC layer in this embodiment works astransparently as possible and the central reordering and reassemblingfunctions are carried out in the PDCP layer. In order to perform thereordering and reassembling, the PDCP layer has to understand thesegment header (SO and LSF) of the MAC layer, since the segmentation isbeing performed in the MAC. The PDCP receives the PDUs from MAC layerand performs central reordering and reassembling, similarly as describedin the above embodiments for the RLC layer. It overlaps common segmentsand sends a status report indicating only the missing part of thesegments, i.e. the part which has not been correctly received by any ofthe eNBs.

When looking at FIG. 17 , it can be seen that the MAC PDUs includesegmentation information as described above, i.e. SO and LSF. However,similarly as for the other embodiments, the segmentation information mayinclude segment number and length of the segments instead. Moreover,FIG. 15 shows PDCP SN usage also in the RLC layer to reduce overhead.However, the present disclosure is not limited thereto and in generalseparate sequence numbers may be used for the PDCP and the RLC layers asit is the case in the LTE currently. As mentioned above, cross-layerdesign may improve the efficiency of the transmissions. In particular,the status report is advantageously transmitted and received on thelayer (RLC) below the coordinating layer (third, PDCP) and provided tothe coordinating layer for matching the received segments and decidingwhich segments are to be transmitted, Moreover, the MAC segmentationinformation may be passed up to the coordinating layer in order toenable re-ordering and re-assembly, as well as the coordination of theretransmissions.

However, it is noted that the present disclosure may still work, evenwhen slightly less efficiently, if the PDCP does not perform theretransmission coordination and if the segments are indeed retransmittedredundantly on each link. Advantageously, in FIG. 17 , the PDCP RX sendsa status report of missing 801 to 1200 bytes. Advantageously, thisstatus report is send to both (in general multiple) eNBs, so thatdiversity is achieved by retransmission over both links. However, thepresent disclosure is not limited thereto and generally, for the purposeof the retransmission, single connectivity may be re-established.

As shown in FIG. 18 , the PDCP TX, upon reception of the status report,takes a complete PDCP PDU (1200 bytes) from the transmission buffer andperforms a re-segmentation (extraction) of the 800 to 1200 bytes whichare indicated by the PDCP status report and then the PDU segment of800-1200 bytes (re-segmented PDU) is delivered to the MAC. The MAC layerof each eNB performs its own segmentation according to the resourceallocation as described in the above embodiments. In this case, as canbe seen in FIG. 18 , the fits MAC entity (transmitting to eNB1) segmentsthe 800-1200 bytes to two MAC PDUs, namely in MAC PDU1 with 800 to 900bytes and a second MAC PDU2 with 901 to 1200 bytes. On the other hand,the second MAC entity (transmitting to eNB2) segments the 800-1200 bytesto a first MAC PDU1 with the bytes 801-1000 and a second MAC PDU2 withthe bytes 1001 to 1200.

In general, there are also alternatives: As described above, the PDCPtakes the complete PDU from retransmission buffer and then performsre-segmentation of the missing packet, which is indicated by PDCP statusreport.

However, alternatively, the PDCP status report may be understood by theMAC layer and therefore, the PDCP passes the complete PDU to the MAC,rather than doing the re-segmentation. The MAC will perform segmentationbased on the PDCP status report then.

Still another possibility is that the PDCP will inform the RLC about themissing part(s) of segments. Afterwards, the RLC layer will send thestatus report to the RLC TX.

Correspondingly, FIG. 19 shows receiving side (network side in thisuplink data transmission example) upon reception of the retransmissionsof FIG. 18 . In particular, in this example, all segments are receivedcorrectly at the MAC and demultiplexed. The RLC basically passes thereceived segments together with the segmentation information receivedfrom the MAC to the PDCP and the PDCP performs the re-ordering andreassembly of all segments received from all nodes of themulti-connection (here eNB1 and eNB2).

FIG. 20 illustrates the transmitting apparatus 2000 t and the receivingapparatus 2000 r being parts of a communication system 2000 andcommunicating over a channel 2090. In particular, the fourth layerprocessing unit 2040 t, the third layer processing unit 2030 t, thesecond layer processing unit 2020 t and the first layer processing unit2010 t perform the processing of the corresponding layers as describedin the embodiments above. The transmitter 2050 transmits via itsantenna(s) the signal mapped onto the physical resources. The receivingapparatus 2000 r correspondingly comprises the fourth layer processingunit 2040 r, the third layer processing unit 2030 r, the second layerprocessing unit 2020 r and the first layer processing unit 2010 r and areceiver 2060 which receives the transmitted signal over its antenna(s).

FIG. 21 exemplifies one of the embodiments of methods according to thepresent disclosure. In particular, at the left hand side, a methodperformed at the data transmitting side is illustrated while on theright hand side a method performed at the data receiving side isexemplified.

The transmitting method may include steps performed by the third layerincluding receiving 2110 t a 3^(rd) layer SDU, generating 2120 t a PDUbased thereon for instance by appending a header and passing 2130 t thePDU to the second layer. The second layer processing then may includereceiving the third layer PDU as a second layer SDU 2140 t, performingsegmentation or concatenation 2150 t as described above, based on thereceived allocation (and in some embodiments also based on the statusreport) and passing the so formed PDU to the first layer in step 2160 t.The first layer processing then includes receiving 2170 t the SDU fromthe second layer, mapping it to the physical resources 2180 t andtransmitting 2190 t.

At the receiver, as a part of the first layer processing, the reception2190 r is performed, then the data are demapped from the physicalresources 2180 r and passed 2170 r to the second layer. The second layerprocessing includes receiving 2160 r the PDU, demultiplexes it 2150 rand passes 2140 r to the third layer for reordering and reassembly (asdescribed above, in one alternative embodiment, the reordering andreassembly is also performed in the second layer). The third layerprocessing includes receiving the PDU 2130 r, performing the reorderingand reassembly 2120 r and passing the reassembled packet to the upperlayers 2110 r.

Moreover, there are embodiments which implement retransmission mechanismon the third layer, including transmission of a status report at thedata receiving side and receiving 2128 t the status report at the datatransmitting side. If the status report includes negativeacknowledgement for some segments (2125 t, “yes”), the re-segmentationis performed on the third layer (alternatively, in some embodiments inthe second layer).

In summary, according to an embodiment of the present disclosure, a datatransmitting node is provided for transmitting data over a wirelessinterface in a communication system to a data receiving node,comprising: a third layer processing unit for performing an automaticrepeat request, ARQ, retransmission according to a status report fedback from the data receiving node and for re-segmenting or not data tobe retransmitted based on segment length information included in thestatus report including adding to the data a segmentation controlinformation; a second layer processing unit for receiving, from thethird layer processing unit, a third layer data unit, segmenting thethird layer data unit based on a resource allocation and forming aplurality of second layer data units including the respective segmentsof the third layer data unit and the segmentation control informationwhich is modified if re-segmentation is to be applied; and a first layerprocessing unit for receiving from the second layer one or more of theplurality of the second layer data units and mapping the one or more ofthe plurality of the second layer data units onto the resourcesallocated for data transmission.

According to another embodiment of the present disclosure, a datatransmitting node is provided for transmitting data over a wirelessinterface in a communication system to a data receiving node,comprising: a third layer processing unit for performing an automaticrepeat request, ARQ, retransmission according to a status report fedback from the data receiving node; a second layer processing unit forreceiving, from the third layer processing unit, a third layer dataunit, segmenting the third layer data unit according to the statusreport and based on a resource allocation and forming a plurality ofsecond layer data units including the respective segments of thesegmented third layer data unit; and a first layer processing unit forreceiving from the second layer one or more of the plurality of thesecond layer data units and mapping the one or more of the plurality ofthe second layer data units onto the resources allocated for datatransmission.

According to another embodiment of the present disclosure, a datareceiving node is provided for receiving data over a wireless interfacein a communication system from a data transmitting node, comprising: afirst layer processing unit for de-mapping one or more of a plurality ofsecond layer data units from the resources allocated for datatransmission and for providing the one or more of the plurality of thede-mapped second layer data units to a second layer processing unit; thesecond layer processing unit for performing de-multiplexing of aplurality of third layer unit segments and segmentation controlinformation from the one or more of the plurality of second layer dataunits, and forwarding the plurality of the demultiplexed third layerunit segments together with the segmentation control information to athird layer processing unit; the third layer processing unit forperforming re-ordering of the plurality of the demultiplexed third layerunit segments and assembly of the demultiplexed third layer unitsegments into a third layer data unit.

Moreover, a method is provided for transmitting data over a wirelessinterface in a communication system to a data receiving node,comprising: performing a third layer processing including performing anautomatic repeat request, ARQ, retransmission according to a statusreport fed back from the data receiving node and for re-segmenting ornot data to be retransmitted based on segment length informationincluded in the status report including adding to the data asegmentation control information; performing a second layer processingincluding receiving, from the third layer processing unit, a third layerdata unit, segmenting the third layer data unit based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isto be applied; and performing a first layer processing includingreceiving from the second layer one or more of the plurality of thesecond layer data units and mapping the one or more of the plurality ofthe second layer data units onto the resources allocated for datatransmission.

Still further, a method is provided for transmitting data over awireless interface in a communication system to a data receiving node,comprising: a third layer processing including performing an automaticrepeat request, ARQ, retransmission according to a status report fedback from the data receiving node; a second layer processing includingreceiving, from the third layer processing unit, a third layer dataunit, segmenting the third layer data unit according to the statusreport and based on a resource allocation and forming a plurality ofsecond layer data units including the respective segments of thesegmented third layer data unit; and a first layer processing includingreceiving from the second layer one or more of the plurality of thesecond layer data units and mapping the one or more of the plurality ofthe second layer data units onto the resources allocated for datatransmission.

Furthermore, a method for receiving data over a wireless interface in acommunication system from a data transmitting node, comprising: a firstlayer processing including de-mapping one or more of a plurality ofsecond layer data units from the resources allocated for datatransmission and for providing the one or more of the plurality of thede-mapped second layer data units to a second layer processing unit; thesecond layer processing including performing de-multiplexing of aplurality of third layer unit segments and segmentation controlinformation from the one or more of the plurality of second layer dataunits, and forwarding the plurality of the demultiplexed third layerunit segments together with the segmentation control information to athird layer processing unit; the third layer processing includingperforming re-ordering of the plurality of the demultiplexed third layerunit segments and assembly of the demultiplexed third layer unitsegments into a third layer data unit.

MAC Subheaders

MAC PDUs are byte aligned bit strings. One MAC PDU includes at least MACsubheaders associated with MAC control elements and/or MAC SDUs, and, ifrequired, padding. A MAC control element is used for signalling betweenthe MAC peers in the eNB and in the UE. A MAC SDU contains data from thehigher layer (RLC), accordingly, MAC SDUs correspond to RLC PDUs. A RLCPDU contains user data from one service. The MAC PDU includes asub-header for each MAC control element and for each MAC SDU.

Each sub-header includes a logical channel ID (LCID). In a sub-headerassociated with a MAC control element, the LCID points at the controlelement type of the respective MAC control element carried. In asub-header associated with a MAC SDU, the LCID indicates the identity ofthe logical channel which the carried respective RLC PDU belongs to.

User Plane Protocol Stack

FIG. 22 shows an exemplary structure of a user plane protocol stack.From top to bottom, the arrangement of different data units in the thirdlayer and the second layer is shown. The top row refers to third-layerSDU, the second row refers to third-layer PDU, the third row refers tosecond-layer SDU, and the bottom row refers to second-layer PDU. In anembodiment shown in the drawing, the third layer corresponds to the RLClayer of the user plane, and the second layer corresponds to the MAClayer of a user plane. Not shown in the drawing is the fourth layer,which in the discussed embodiment corresponds to the PDCP layer of theuser plane. The third layer and the second layer are visually separatedby a dashed line.

Data units are passed from the RLC layer to the MAC layer throughlogical channels (LC). In FIG. 22 , two logical channels with logicalchannel identifiers LCID1 and LCID2 are shown. Signaling and user datapertaining to the channel with LCID1 are marked by solid line frames,and data elements associated with LCID2 are marked by dashed lineframes. As can be seen in the drawing, different amounts of data unitsmay be provided through different logical channels. In the exampleshown, in the top-row associated with third-layer SDUs, two data unitsof the top row corresponding to third-layer SDU belong to a firstlogical channel with LCID1 (the data units labeled “PDCP PDU1” and “PDCPPDU2”), whereas one data unit belongs to a second logical channel withLCID2 (“PDCP PDU1”). Since third-layer SDUs can be identified by meansof the corresponding logical channel, two third-layer SDUs operated bytwo different logical channels have the same label, “PDCP PDU 1” in thedrawing. However, the present disclosure is not restricted to the caseshown in FIG. 22 ; alternatively, different logical channels may operatethe same amount of data to be allocated to a TB. There may be also onlyone logical channel or more than two logical channels.

Through the different logical channels with identifiers LCID1 and LCID2,fourth-layer PDUs (labeled PDCP PDU1, PDCP PDU2, and PDCP PDU1) arereceived by the third layer processing unit from the fourth layerprocessing unit to be processed as third-layer SDUs. By adding athird-layer header including a sequence number (referenced as “RLC SN”)to each of the fourth-layer PDUs corresponding to third-layer SDUs, thethird layer processing unit generates third-layer PDUs each of whichconsists of a third-layer header and a third-layer SDU. The third-layerPDUs are then forwarded to the second layer which receives them assecond-layer PDUs. Although the third-layer SDUs shown in the second roware identical to the second-layer PDUs shown in the third row, theseidentical data units are shown twice in FIG. 22 , which is only forreasons of illustration.

The second-layer processing unit receives second-layer SDUs from thethird layer and generates a second-layer PDU, which is shown in thebottom row of FIG. 22 , by concatenating one or more second-layer SDUswith some second-layer control information and possibly padding. In thegeneration of the second-layer PDU, different data elements areconcatenated. In particular, second-layer subheaders are provided forthe respective user data and control elements, labeled respectively “MACLCID 0+L”, “MAC LCID 1+L”, “MAC LCID 2+L”, “MAC LCID P”. Here thelabeling indicates that the subheader carries prioritization controlinformation corresponding to the respective LCIDs (since priorities areassigned to the respective LCIDs) and the length information (L). Thesecond-layer control elements (labeled “MAC CE”) may be further insertedinto the second-layer PDU as well as padding, if necessary. In the FIG.,the padding at the end of the MAC PDU is shown with a correspondingsubheader for the padding (“MAC LCID P”). A case in which padding ispreceded by a corresponding subheader may be the Padding BSR which maybe included in a MAC PDU instead of mere padding. For the Padding BSR,see also 3GPP TS 36.321 v 13.3.0, section 5.4.5.

It is noted that in some LTE versions, padding may have thecorresponding subheader assigned, depending on the length of thepadding. In particular, padding is inserted at the end of MAC PDU exceptwhen single byte or two bytes padding required. When single-byte ortwo-byte padding is required, one or two MAC PDU subheaders representingthe padding are placed at the beginning of the MAC PDU before any otherMAC PDU subheader.

In terms of the LTE terminology, FIG. 22 shows PDCP PDUs (representingrespective RLC SDUs) of two different logical channels concatenated intoa single MAC PDU. In this case, after concatenating the three MAC SDUscorresponding to the two logical channels and prepending to each of themthe corresponding MAC subheader, there still is some place left in theallocated resources. In this place, one or more MAC CEs areadvantageously inserted. If there is still some place left, padding isapplied. Providing respective MAC subheaders instead of a single MACheader for the MAC PDU enables at least partial pre-processing of theMAC PDU.

Correspondingly, the user plane protocol stack shown in FIG. 22 anddiscussed above is an exemplary user plane protocol stack for NR. Withsuch a user plane, pre-processing of third-layer headers andsecond-layer subheaders is possible. In particular, a second-layer SDUwith its associated second-layer subheader can be delivered to the firstlayer before a complete TB (the complete MAC PDU) has been built. This,on the other hand, enables processing delay reduction.

The advantages related to the enabling of processing delay reductionmentioned above result from a suitable second-layer (MAC) PDU format, asis provided by the embodiments of the present disclosure. In thefollowing, different alternative configurations of second-layer PDUformats are described with respect to FIGS. 23 to 30 . Although it isassumed in these FIGS. that the second layer corresponds to the MAClayer, the present disclosure is not restricted to the case in which thesecond layer is the MAC layer.

FIG. 23 is a schematic drawing showing an exemplary second-layer PDUcorresponding to the user plane protocol stack described with respect toFIG. 22 . The second-layer PDU includes two second-layer SDUs, twosecond-layer control elements (CE), the corresponding four respectivesecond-layer subheaders, and padding. A respective second-layersubheader is associated with each of the second-layer SDUs and with eachof the second-layer control elements. Each of the second-layersubheaders precedes the second-layer SDU or, respectively, thesecond-layer control element with which it is associated. Thisassociation is indicated in the drawing by the arrows pointing from eachsecond-layer subheader to the respective second-layer control element orsecond-layer SDU. The same arrow notation is used in the FIGS. 24 to 30to denote the association of a second-layer subheader. In thesecond-layer PDU format shown in FIG. 23 , the second-layer controlelements are placed before all the second layer SDUs, i.e. before any ofthe second-layer SDUs. In other words, each of the second layer controlelements precedes each of the second-layer SDUs. The padding is placedat the end of the second-layer PDU. However, in this second-layer PDUformat, padding is a merely optional component of the second-layer PDU,only applicable if there is some remaining place left in the MAC PDUlength corresponding to the allocated physical resources, the remainingplace being too small to accommodate any other MAC SDU or MAC CE to betransmitted. This also applies to any second-layer PDU format accordingto any embodiment to be described in the remainder of this description.

In FIG. 23 , number of second-layer PDUs and the number of second-layercontrol elements are both two. However, the present disclosure is notlimited to a particular number of second-layer control elements or aparticular number of second-layer SDUs. Rather than suggesting aparticular number of second-layer control elements or second-layer SDUs,the drawing illustrates the particular order of second-layer subheaders,second-layer SDUs, second layer control elements, and the padding withinthe second-layer PDU.

As already mentioned with reference to FIG. 22 , the arrangement of FIG.23 provides the advantage that each MAC CE or MAC SDU with therespective corresponding subheader can be individually provided to thelower layer without waiting for the entire MAC PDU to be assembled.

A disadvantage of the second-layer PDU format of FIG. 23 is that as anysecond-layer control elements are placed before any second-layer SDUs,the second-layer processing unit can only deliver available second-layerSDUs to the physical layer after the second-layer control elements havebeen computed. However, in order to compute some MAC CEs, calculationssuch as prioritization procedure or the like should be terminated. Onthe other hand, preparation of some MAC SDUs may take less time.However, they cannot be provided to the physical layer before the MACCEs have been calculated.

Efficient MAC Control Elements Signaling

In order to address the above mentioned disadvantage, FIG. 24 shows anadvantageous embodiment of a MAC PDU, in which any MAC SDU precedes anyMAC CE. In particular, the MAC PDU 2400 starts with a first MAC SDU 243a preceded by a subheader 241 a associated therewith. The first MAC SDUis followed by a second MAC SDU 243 b with is respective header 241 b.In this example there are only two MAC SDUs, the logical channel ID(priority) of which may be signaled in their respective subheader.However, in the present embodiment, the MAC PDU may include more thantwo MAC SDUs. The MAC PDU 2400 further comprises a MAC subheader 242 aassociated with a first MAC CE 244 a followed by the MAC subheader 242 bassociated with a second MAC CE 244 b. The MAC subheaders 242 a, 242 bprecede their respective MAC CE, 244 a or 244 b, with which they areassociated. As shown in the drawing, the MAC CE 244 a and the MAC CE 244b as well as their respective MAC subheaders 242 a and 242 b follow anyof the MAC SDU 243 a and the MAC SDU 243 b and their respectivesubheaders 241 a, 241 b.

The present embodiment is not limited to the case in which there are twoMAC CEs. There may be only one MAC CE or more than two MAC CEs. Further,a case is shown in the drawing in which the number of MAC CEs is equalto the number of MAC SDUs. However, the number of MAC CEs may bedifferent from the number of MAC SDUs. In a MAC PDU according to thepresent embodiment, there may be fewer MAC CEs than there are MAC SDUsor, alternatively, there may be more MAC CEs than MAC SDUs. It is afeature of the embodiment that any MAC CE and any MAC subheaderassociated with any MAC CE follows any MAC PDU or any subheaderassociated with any MAC PDU. Optionally, padding 245 may be added. Ifthe complete resources of a TB are used for MAC SDUs, MAC CEs, and theirrespective MAC subheaders, padding may be omitted.

In general, padding is inserted if, after mapping the MAC SDUs and theMAC CEs together with their respective MAC subheaders, there are stillsome free resources among the resources allocated for the transmissionand these free resources are not enough to convey any further MAC CE orMAC SDU.

Thus, a data transmitting node for transmitting data over a wirelesschannel to a data receiving node in a communication system 3100 maygenerate the MAC PDUs as exemplified in FIG. 24 , thereby enablingprocessing delay reduction. In particular, such a node may correspond tothe device 3100 t illustrated in FIG. 31 , and comprise a second-layerprocessing unit 3120 t and a first-layer processing unit 3110 t. Thesecond-layer processing unit 3120 t is suitable for receiving, from athird layer processing unit 3130 t, at least one second-layer servicedata unit, SDU, to be mapped onto a resource allocated for datatransmission, and for generating a second-layer PDU. Such a second-layerPDU generated by the second-layer processing unit includes the at leastone second-layer SDU received from the third layer and at least onesecond-layer control element, the at least one second-layer controlelement following any of the at least one second-layer SDU. Thefirst-layer processing unit 3110 t is suitable for receiving thesecond-layer PDU generated by the second-layer processing unit andmapping the second-layer PDU onto the resource allocated for datatransmission.

On the other hand, a receiving node for receiving data over a wirelesschannel from a data transmitting node in a communication system 3100node may receive and process the MAC PDUs as exemplified in FIG. 24 ,thereby enabling processing delay reduction. In particular, such a nodemay correspond to the device 3100 r illustrated in FIG. 31 , andcomprise a first-layer processing 3110 r unit and a second-layerprocessing unit 3120 r. Therein, the first-layer processing unit 3110 ris suitable for de-mapping at least one second-layer protocol data unit,PDU, from a resource allocated for data reception. Further, thesecond-layer processing unit 3120 r is suitable for receiving andparsing the second-layer PDU de-mapped by the first-layer processingunit. Such a second-layer PDU received and parsed by the second-layerprocessing unit includes at least one second-layer SDU, to be forwardedto a third layer processing unit 3130 r included in the data receivingnode 3100 r, and at least one second-layer control element, the at leastone second-layer control element following any of the at least onesecond-layer SDU.

Advantageously, the second-layer PDU to be generated by the second-layerprocessing unit of the data transmitting node and, correspondingly, thesecond-layer PDU to be received and parsed by the second-layerprocessing unit of the data receiving node further include a respectivesecond-layer subheader associated with each of the at least onesecond-layer SDU, and a respective second-layer subheader associatedwith each of the at least one second-layer control element. As mentionedabove, providing a plurality of respective MAC subheaders within the MACPDU rather than a single MAC header enables forwarding portions of theMAC PDU to the lower layers rather than the entire MAC PDU. This, on theother hand, allows for reducing the delay since some portions of the MACPDU may be earlier processed by the lower layers.

It is noted that in some systems, subheaders for the MAC CEs and/or SDUsmay be unnecessary. In LTE like systems, a subheader may typicallyinclude a channel type indication and a length indication. The channeltype indication may serve for prioritization of the particular MAC PDUportions. The length indication specifies the length of thecorresponding data portion such as length of the MAC SDU and/or MAC CE.However, in some systems, the MAC SDU may have a predefined length or alength configured in another way, so that the length indication may notbe necessary, either.

FIG. 25 illustrates an example of a subheader format for a MAC SDU,which is similar to the format known from the current LTE standard (seealso 3GPP TS 36.321 v 13.3.0 Section 6.2.1). A MAC PDU having the sameformat as shown in FIG. 24 is shown, and the format of a MAC subheaderis exemplified by a MAC subheader associated with a MAC SDU (labeled MACSDU2 in the drawing). This MAC SDU corresponds to the MAC SDU 243 b, andits associated MAC subheader corresponds to the MAC subheader 241 bshown in FIG. 24 . Accordingly, a MAC subheader includes a reserved bits(R), a format2 field (F2), an extension field (E), a logical channel ID(LCID) field. It further includes a length field (L) and a format field(F) if the subheader is associated with a MAC SDU or a variable-sizedMAC control element.

The extension field E may be a one-bit field. In the LTE, the one rowR/F2/E/LCID is one octet (byte, i.e. 8 bits) long, wherein the R-fieldis one bit long, the F2 field is one bit long, the E-field is one bitlong and the LCID is 5 bits long. Already in the LTE, F2=1 indicatesthat the size of the corresponding MAC SDU or variable-sized controlelement is larger than 32767 bytes (corresponding to 15 bits lengthfield), and that the subheader is not the last subheader in the MAC PDU.The extension field E indicates the presence of another MAC subheader inthe PDU. In particular, a value E=1 indicates that at least one more MACsub-header including at least R/F2/E/LCID fields (and thus also possiblythe corresponding SDU or CE) follows in parsing direction in the MACPDU. The parsing direction in the LTE is assumed to be from thebeginning of the MAC PDU (starting with the header) towards the end.This is also the case for FIG. 25 , in which the parsing direction isfrom left to right.

In FIG. 24 such additional octet is shown in the second row of thesubheader with the fields F and L. In general, if the header has onlyone octet, the length L field is not present. Thus, the length of theMAC SDU cannot be signaled. In LTE, a second octet is not included inthe MAC subheader if the MAC subheader is associated with a fixed-lengthMAC control element. In this case, the length of the fixed-length MACcontrol element is known from the LCID which specifies type of the MACcontrol element. The F field indicates the length of the L field, which,in LTE, may be 7 bits or 15 bits long (thus extending over either one ortwo octets). The R field is reserved in the current LTE standard but maybe replaced with another indicator or indicators in the upcomingversions of the standard. In other words, in a receiver workingaccording to the current standard, the R-field is ignored.

As will be discussed below, the parsing direction may generally be fromthe start of the MAC PDU towards the end of the MAC PDU or vice versa,depending on the format of the MAC PDU.

For the fields of the MAC subheader in LTE, see also 3GPP TS 36.321 v13.3.0 Chapter 6.2.1.

The LCID field has, for example, 5 bits as in LTE, and indicates thesubheader type and the logical channel or, in case the subheader isassociated with a control element, the control element type. Here, thesubheader type means whether the subheader is a MAC CE subheader or aMAC SDU subheader or anything else (e.g. reserved, padding, etc.).Subheaders of the respective MAC CE types define the MAC CE typeuniquely. For instance, “11101” stands for short BSR, “11010” stands forPHR, whereas “11011” stands for C-RNTI and “11111” stands for padding.

The length field L in LTE may have 7 or, alternatively, 15 bits, and itindicates the length of the MAC SDU, or respectively, the length of theMAC control element, depending on whether the sub-header is associatedwith a MAC control element or a MAC SDU. In the L field, the length ofthe MAC SDU or, respectively, the MAC control element is given in bytes.Further, the format field F may be a 1-bit field indicating the lengthof the L field. For example, a value F=0 may indicate that the L fieldhas 7 bits, whereas F=1 may indicate that the L field has 15 bits.

However, it is noted that the present disclosure is not limited to thesubheader format of the current LTE standard. The lengths and values offor the E, LCID, F and L field are examples corresponding to anadvantageous implementation of a MAC subheader. However, a MAC subheaderhaving a structure corresponding to an embodiment of the presentdisclosure may be implemented using different field lengths or variablevalues.

An exemplary MAC PDU according to an exemplary embodiment of the presentdisclosure is shown in FIG. 26 . The format of the MAC PDU correspondsto the MAC PDU format shown in FIG. 24 . The MAC PDU shown in FIG. 26includes MAC SDUs and a MAC control element, all of which are precededby their respective MAC subheaders. At the end of the MAC PDU, paddingis shown as an optional component. In this example, only one MAC controlelement is shown, namely a BSR MAC control element. However, incorrespondence with the MAC PDU format illustrated in FIG. 24 , the MACcontrol element and its respective MAC subheader are placed after eachMAC SDU (MAC SDU1 and MAC SDU2 in the drawing) and their respective MACsubheaders. Although not shown in the drawing, instead of a BSR MACcontrol element, a different type of MAC control element plus itsassociated subheader may also be placed after each MAC SDU and therespective MAC subheader of each MAC SDU included in a MAC PDU. Forexample, the MAC control element may also be a power headroom report,BSR (short, long or truncated) or C-RNTI. Accordingly, the second-layercontrol element is any one of a buffer status report, C-RNTI and a powerheadroom report and each second-layer subheader associated with anybuffer status report, C-RNTI or power headroom report is placed aftereach of the at least one second-layer SDU.

In the MAC PDU according to the embodiment shown in FIG. 24 , MAC CEs(for example, BSR MAC CEs, and PHR MAC CEs) and their associated MACsubheaders are always placed after any MAC SDUs, while MAC SDUs andtheir associated MAC subheaders are located at the beginning of a MACPDU corresponding to a TB. Therefore, the beginning of the MAC PDU doesnot depend on the MAC CEs. For instance, it does not depend on thecomplete outcome of LCP in the case of the MAC CE being a BSR, and thecalculation of the PHR depends upon PHY inputting this value to MAC.This independence allows for sending the beginning of MAC PDU (when thefirst MAC SDU is ready) to the first-layer (PHY) processing unit evenbefore the MAC PDU has been fully constructed. Accordingly, the second(MAC) layer can start forwarding packets to the first (PHY) layer whenthe first second layer SDU is ready, and the second layer processingunit does not need to wait until it has assembled the entire secondlayer PDU before forwarding packets belonging the to the second layerPDU to the lower layer(s). It is beneficial for transmission processingdelay reduction and allows more processing time for sender, i.e. thedata transmitting node, to compute BSR and PHR, as both BSR MAC controlelements and MAC PHR control elements are located at the end of a TB,i.e. after any MAC SDUs included in the MAC PDU.

An advantage of using a MAC PDU format as shown in FIGS. 24 and 26 and,correspondingly, a MAC subheader structure as shown in FIG. 25 , is thatmost MAC subheaders and MAC SDUs except for the last one subjected tosegmentation can be pre-processed. However, while such a MAC PDU formatis transmitter friendly however, it might be important for the receiverto receive and process certain types of MAC CEs as soon as possible i.e.activation/de-activation MAC CEs and UE contention resolution MAC CEs indownlink (transmitted from eNB to the UE) or C-RNTI in uplink (from theUE to the eNB). Accordingly, in LTE this was the main reason to placeMAC CEs before any MAC SDUs in a MAC PDU.

An early processing of MAC control elements of certain types (such asactivation/de-activation MAC CEs and UE contention resolution MAC CEs inDL or the C-RNTI in UL) can be achieved through an embodiment of thepresent disclosure which is illustrated in FIG. 27 . In the drawing, aMAC PDU is shown in which a MAC control element and its associatedsubheader are placed at the beginning of the MAC PDU, the MAC subheaderpreceding the MAC control element with which it is associated (in thedirection of parsing which is here from the beginning of the MAC PDUtowards the end). In particular, the MAC control element shown in thedrawing is an activation/deactivation MAC CE. Theactivation/deactivation MAC CE precedes any MAC SDU and any MACsubheader associated with a MAC SDU. In the drawing, two MAC SDUs andtheir associated MAC subheaders are shown. However, the embodiment ofthe disclosure is not limited to the number of MAC SDUs being two.Alternatively, there may be only one MAC SDU or more than two MAC SDUsincluded in the MAC PDU. Although the MAC control element shown in thedrawing is an activation/deactivation CE, a UE contention resolution MACCE and its associated subheader or the C-RNTI with its subheader mayinstead or in addition be placed at the beginning of a MAC SDU, i.e.before any MAC SDU and any MAC subheader associated with a MAC SDU. Asshown in the drawing, a MAC SDU in the present embodiment may end withpadding, if necessary.

In other words, depending on the type of the MAC CE, the MAC CE isplaced either before or after any MAC SDUs when assembling the MAC PDU.The MAC CE type may be defined in the respective MAC CE subheader, forinstance within the LCID field.

Different types of MAC CEs may be included in a MAC PDU, of which onetype is advantageously placed at the beginning of the MAC PDU, i.e.before any MAC SDU, and another type is advantageously placed at the endof the MAC PDU, i.e. after any MAC SDU. Therefore, in an exemplaryembodiment of the disclosure, in addition to at least one second-layercontrol element which is placed after any second layer SDU, thesecond-layer PDU further includes a second-layer control element whichis placed before any second-layer SDU. A second-layer subheaderassociated with the second-layer control element placed before anysecond layer SDU may further be included and placed before therespective second-layer control element at the beginning of thesecond-layer PDU.

An example of a MAC PDU format according to this embodiment isillustrated in FIG. 33 . At the beginning of the MAC PDU, there is a MACCE, namely a C-RNTI MAC CE, which is preceded by the subheaderassociated with this C-RNTI MAC CE. After the C-RNTI MAC CE, two MACSDUs are included in the MAC PDU, each of which is preceded by arespective associated MAC subheader. However, the disclosure is notlimited to the number of second-layer SDUs being two, there may be oneor more than two second-layer control elements. After the last MAC SDU,a further MAC CE is included and preceded by its respective associatedMAC subheader. In the example shown in the drawing, this MAC CE is a BSRMAC CE. However, the disclosure is not limited to the MAC CE before anyMAC SDU being a C-RNTI MAC CE, and the MAC CE after any MAC SDU being aBSR MAC CE. Instead of a C-RNTI, there may be, for example, anactivation/deactivation MAC CE, and instead of the BSR MAC CE, there maybe, for example, a MAC PHR control element. Furthermore, instead of oneMAC CE placed before and one MAC CE placed after each MAC SDU, there maybe two or more MAC CEs placed before and/or after any MAC SDU.Optionally, after the MAC CE placed after each MAC SDU, padding isincluded at the end of the MAC PDU. The present disclosure is notlimited to the CEs currently defined by the LTE but is also applicableto any CEs of any systems. In general, CEs which require longercalculation time or input from other layers may be advantageously placedat the end of the MAC PDU, while CEs which are available may be placedat the beginning of the MAC PDU.

A MAC PDU format as shown in FIG. 33 may advantageously be used in atransmitter/receiver system that allows forwarding of parts of a TBinstead of forwarding only complete TBs to lower/higher layers. Forinstance, the TB may be subdivided into a plurality of parts whichbecome individual codewords and may also be provided by respective CRCs.

Thus, when the MAC PDU is divided among different parts of the TB andMAC CEs such as C-RNTI MAC CEs are placed at the beginning of the MACPDU, these MAC CEs can be processed at the transmitter by the PHY layerwithin codewords without having to wait for completion and forwarding ofthe entire TB.

At the receiver side, one or more of the codewords may be receivedindividually and their CRC may be checked. Then, the PHY may forward theindividual correctly received codewords to the MAC before the entire TBhas been received correctly. This is advantageous, since the MAC CElocated at the beginning of the MAC PDU (e.g. the C-RNTI) may beextracted in the MAC layer before the remaining TB codewords have beencorrectly received and passed to the MAC. However, if not all codewordspertaining to the TB have been received correctly, i.e., the TB has notbeen received successfully, the entire TB is discarded, i.e. also thealready parsed (preprocessed) parts such as MAC CEs and MAC SDUs.

It is noted that the above layer processing is exemplary. The presentdisclosure may also be applied to other system designs in which thetransport block corresponds to one codeword and is not processed inmultiple individual parts.

Accordingly, the receiver does not need to wait until the end of the TTIbefore it can process the respective MAC CE. Thus, for the C-RNTI MAC CE(or another MAC CE such as an activation/deactivation MAC CE),preparation processing is possible.

Thus, it may be advantageous if the data transmitting and/or receivingdevice is capable of generating and transmitting or receiving both, theMAC CEs located before the MAC SDUs and MAC CEs located after the MACSDUs. It is noted that in general, the data transmitting device may bethe terminal in uplink or the base station in downlink.

In an embodiment of the present disclosure, a data transmitting node fortransmitting data over a wireless channel to a data receiving node in acommunication system may include a second-layer processing unit which isconfigurable to generate different types of second-layer PDUs. Inparticular, it may be suitable for generating a first-type second-layerPDU which includes at least one second layer SDU and at least one secondlayer control element, the at least one second-layer control elementfollowing any of the at least one second-layer SDU. It may be furtherconfigurable to generate a second-type PDU which includes at least onesecond layer SDU and at least one second layer control element, the atleast one second-layer control element preceding any of the at least onesecond-layer SDU.

As discussed above, some MAC control elements are advantageously placedafter any MAC SDUs in a MAC PDU, whereas other MAC control elements areadvantageously placed before any MAC SDU. For this reason, an embodimentof the present disclosure provides a second-layer processing unit whichis configurable to generate a second-layer PDU including atype-switching second-layer control element (type-switching MAC CE)indicating whether the second-layer PDU including the type-switchingsecond-layer control element is a first-type second-layer SDU or asecond-type second-layer SDU. The type-switching second-layer controlelement precedes any second-layer SDU and any second-layer controlelement different from the type-switching second-layer control element.The second-layer PDU further includes a second-layer subheaderassociated with and preceding the type-switching second-layer controlelement. The second-layer subheader associated with the type-switchingsecond-layer control element precedes the second-layer type-switchingcontrol element. However, it is noted that the explicit type switchingMAC CE is only an example. Such MAC CE is not necessary to decidewhether to generate a MAC PDU with the CEs at the beginning or at theend. Such decision may be made solely based on the type of the MAC CE(s)to be included into the MAC PDU according to some predefined (fixed)rules.

Moreover, it is noticed that in general, a MAC PDU may also include bothMAC CEs located before the (any) MAC SDUs and MAC CEs located after anyMAC SDUs. There may also be a difference between the uplink anddownlink. For instance, in downlink, the MAC CEs may always be locatedat the beginning (i.e. preceding any SDUs) whereas in uplink the type ofMAC CE determines whether it is mapped before or after the SDUs.

In general, in the downlink, a data transmitting node for transmittingdata over a wireless channel to a data receiving node in a communicationsystem may be a base station. A data receiving node for receiving dataover a wireless channel from a data transmitting node in a communicationsystem in downlink may be a UE. As described above, for the uplink, thedata transmitting node may be a UE and data receiving node may be thebase station (eNB).

Generally, a UE and/or the base station may be capable of operating asboth the data transmitting and the data receiving node. In particular,the UE may be capable of generating the MAC PDU with CEs placed afterany SDUs as well as capable of receiving MAC PDUs with MAC CEs placed atthe beginning of the MAC PDU. Similarly, the base station may be capableof transmitting MAC PDU with CEs at the beginning and receiving MAC PDUwith CEs at the end. However, it is noted that the present disclosure isnot limited to such combinations and both directions may support or beconfigurable to support either or both of placing MAC CEs at the end orat the beginning of the MAC PDU, possibly depending on the type of theMAC CEs. It is noted that in general, it is also possible to include MACCEs on both ends of the MAC PDU, depending on their type.

In the embodiments illustrated in FIGS. 23 to 27 , MAC subheaders areplaced respectively before the MAC SDU or the MAC control element theyare associated with. This arrangement of MAC subheaders in a MAC PDUallows the MAC subheaders to be processed as early as possible by areceiver, provided the MAC PDU is parsed in the direction from thebeginning to the end by the receiver (the direction pointing from leftto right in FIGS. 23 to 30 ). However, in some cases it may beadvantageous to start parsing a MAC PDU starting from the ending of theMAC PDU towards the beginning (in the figures from right to left). Inparticular, when control elements are available at the end of a MAC PDU,they can be processed early at the receiver, if the MAC PDU is parsedstarting from the end.

When a receiver parses a MAC PDU from its end (backward), a MACsubheader associated with a MAC control element can be processed earlyif it is placed after the respective control element (or, in otherwords, before the respective control element in the direction ofparsing). To achieve such an early processing of a MAC subheaderassociated with a MAC control element, an embodiment of the presentdisclosure provides a data transmitting including a second-layerprocessing unit for generating a second-layer PDU including at least onesecond-layer SDU and at least one second-layer control element andsecond-layer subheaders associated respectively with the second-layerSDU and the second-layer control element, wherein at the at least onesecond-layer SDU is preceded by the respective associated subheader andthe at least one second-layer control element is followed by therespective associated subheader.

The format of such a second-layer PDU is illustrated in FIG. 28 . Inparticular, the drawing shows a MAC PDU including two MAC SDUs, MAC SDU1and MAC SDU2. MAC SDU1 and MAC SDU2 are directly preceded by theirrespective associated subheader. The number of MAC SDUs shown in thedrawing is only exemplary. Alternatively there may be one MAC SDU, threeMAC SDUs ore more than three MAC SDUs included in the MAC PDU. The MACPDU further includes two MAC control elements, MAC CE1 and MAC CE2 thatfollow each MAC SDU and each subheader associated with a MAC SDU, andMAC subheaders respectively associated with these MAC control elements.Padding may also be included in the MAC PDU.

However, if a receiver starts parsing a MAC PDU at its end, theprocessing of MAC control elements and their associated subheaders isdelayed when the padding is placed at the end of the MAC PDU, i.e. afterany MAC control element. Thus, instead of placing the padding at theend, it may be placed between the MAC SDUs with their associatedsubheaders and the MAC control elements and their associated subheaders.Such location is also beneficial since when starting the parsing at theend of the PDU, the length of the padding is generally not known so thatthe parsing is not possible without obtaining the padding lengthinformation in some way (for instance by signaling information).

An example of this arrangement of the padding is shown in FIG. 28 ,where the padding is directly preceded by MAC SDU2 and directly followedby MAC CE1. The subheader associated with MAC CE1 is placed after MACCE1, and the subheader associated with MAC CE2 is placed after MAC CE2.This corresponds to pre-pending the subheader to the respective MAC CEin the parsing direction, which is here reversed, i.e. from the end ofthe MAC PDU to the beginning, at least for all MAC CEs. It is noted thatthe MAC SDUs may be parsed in the usual (forward) direction from thebeginning towards the end of the MAC PDU.

For example, the two MAC control elements may be a BSR MAC controlelement or a PHR MAC control element. The disclosure is not limited tothe MAC PDU having two MAC control elements. Alternatively, there may bethree or more MAC control elements ore one MAC control element, which,for example, may be a BSR MAC control element or a PHR MAC controlelement.

In order to parse a MAC PDU in an efficient and time-saving way, it ishelpful if the receiver can determine at an early stage of parsing ifMAC control elements are available in the MAC PDU. Especially if the MACCEs are located at the end of the MAC PDU, with such an indication, thereceiver may start parsing the MAC CEs from the end of the MAC PDTbackwards. Information on the availability of a further MAC controlelement can be included in a MAC subheader.

For this reason, in an exemplary embodiment, the first second-layersubheader comprised by the second-layer PDU as discussed previouslyincludes a presence indicator indicating whether the second-layer PDUincludes at least one second-layer control element.

Alternatively, all of the second-layer subheaders comprised by thesecond-layer PDU may include the presence indicator. This solutionenables maintaining the subheader format independent of the position ofthe SDU/CE within the PDU. In this way, it is also compliant with theMAC subheader in current the LTE specifications. On the other hand,including the presence indication only into the first subheader of theMAC PDU may be more efficient regarding the resource utilization.

An example of such a presence indicator is shown in FIG. 29 . In thedrawing, a MAC PDU format is illustrated which is similar to the MAC PDUformat shown in FIG. 28 . Accordingly, at the beginning of the MAC PDUthere is a MAC subheader associated with and preceding a MAC SDU, and atthe end there is a MAC subheader associated with and following a MACcontrol element. For the MAC subheader at the beginning and the MACsubheader at the end of the MAC PDU, the structure of the MAC subheaderis further illustrated. As already shown in FIG. 25 , the MAC subheadersinclude a reserved bit (R), an F2 bit an extension field (E), and aLCID. The configurations of R, F2, E, and LCID are same as theconfigurations discussed with respect to FIG. 25 . The first MACsubheader, which is associated with a MAC SDU, further includes a secondoctet comprising an F field and an L field. Such a second octet is notshown for the last MAC subheader shown in the drawing. It can be assumedthat this MAC subheader is associated with a fixed-length MAC CE ofwhich the size is known based on the LCID, although the embodiment alsoincludes the case of variable-sized control elements in which a secondoctet and in some cases a third octet must be included in the MACsubheader. However, the first reserved bit is now used to indicate ifthere are MAC control elements in the MAC PDU. Here it is assumed thatif there are MAC CEs (at least one) in the MAC PDU, they are placed atthe end. Accordingly, the presence indicator can be used to instruct thereceiver to parse the MAC CEs (and their respective headers) from theend of the MAC PDU in the backward direction, i.e. from the end of theMAC PDU. Accordingly, one of the R bits included in the MAC subheader atthe beginning and/or all MAC subheaders of the MAC PDU is set by thetransmitter.

For example, as shown in FIG. 29 , R=1 means that MAC control elementsare available in the MAC PDU and R=0 means that no MAC control elementsare available. In the drawing, an R bit in both the first and the lastMAC subheader of the MAC PDU is shown to be set R=1, assuming that theremaining subheaders have the same format and R field also set (R=1).However, the disclosure is not limited to the case in which an R bit inall MAC subheaders is set to one. Alternatively, for example, only an Rbit in the first MAC subheader may be set to indicate whether the MACPDU includes a MAC control element. In other words, it is sufficient ifthe R field is presented in the starting subheader, i.e. the subheaderwhich is parsed first, however it can also be set in all subheaders.

In FIG. 29 , a case is shown in which the E bit in the last MACsubheader of the MAC PDU is set to 1. As discussed above with regard tothe structure of the MAC subheader, a value E=1 indicates that at leastone more MAC subheader is present in parsing direction. Since theparsing starts from the end, the at least one more MAC subheader can beidentified with the MAC subheader associated with the MAC controlelement before the last MAC control element (which corresponds to MACcontrol element “CE1” from FIG. 28 ). Thus, in this drawing, the rightutmost MAC subheader has the E field set to 1 meaning that thecorresponding MAC CE is followed (in the backward parsing direction) bya second subheader associated with a second MAC CE. In the secondsubheader, the E-field is set to 0 since in the backward parsingdirection, there is no further subheader, but rather only the (optional)padding.

It is also noted that the parsing of the MAC PDU of FIG. 29 at thereceiver starts with the first subheader of the first SDU. Since R=1,the parsing then advantageously continues from the end of the MAC PDUbackward as described above. After the MAC CEs are extracted, theparsing of the SDUs may be resumed from the beginning (left hand side ofthe drawing). However, it is noted that this is only an advantageousexample of the parsing. The MAC PDU format also allows for parsing theSDUs first and then parsing the MAC CEs from the end towards thebeginning of the MAC PDU.

Thus, the present disclosure also provides a receiver that is able tostart parsing a MAC PDU from the beginning when no MAC control elementsare available, and from the ending when at least one MAC control elementis available. In an embodiment, a data receiving node includes a secondlayer processing unit for receiving and parsing a second-layer PDU,wherein the second layer processing unit parses the second-layer PDUstarting from the end of the second-layer PDU when the presenceindicator indicates that at least one second-layer control element isincluded in the second-layer PDU. For example, the second-layerprocessing unit of the receiver may be configured to parse asecond-layer PDU starting from the beginning by default. Thus, when itstarts parsing, it evaluates the presence indicator (such as onepredefined R bit in the current LTE specification) in the firstsubheader. If the R bit has the value R=1, indicating that a MAC controlelement is included in the MAC PDU, it parses the MAC PDU from its end,deviating from the default setting. It is noted that using the reservedbit R is an advantageous option to provide a presence indicator forindicating whether in the MAC PDU there are MAC CEs present. However,the present disclosure is not limited thereto and the presence indicatormay be introduced in another way, for instance, by providing a longerMAC subheader. As also mentioned above, the present disclosure is notlimited to the format of the subheader as defined by the LTE.

Alternatively, the second-layer processing unit may be configured tostart parsing the MAC PDU from the end by default. In this case, when itstarts parsing, it evaluates the MAC subheader at the end of the MACPDU. When it evaluates the R bit in this subheader and detects the valueR=1 indicating that there are MAC control elements in the MAC PDU, itcontinues parsing the MAC PDU from the end.

When the MAC PDU is parsed from the end, the individual octets of MACsubheaders and MAC control elements may be ordered from both directions.In other words, if the MAC PDU is parsed in backward direction, the bitordering within the individual MAC subheaders and MAC CEs which are tobe parsed in backward direction may or may not be also reversed.However, the direction in which the receiver reads the individual MACsubheaders and MAC control elements must be known to the receiver.

Thus, in an embodiment, a transmitting node is disclosed, which includesa second-layer processing unit for generating a second-layer PDUincluding at least one second-layer subheader and at least onesecond-layer control element, and subheaders associated respectivelywith the at least one second-layer SDU and the at least one second-layercontrol element, wherein the at least one second-layer SDU is precededby the respective associated subheader and the at least one second-layercontrol element is followed by the respective associated subheader.

The MAC PDU format shown in FIGS. 28 and 29 implicates advantages thatare associated with both the receiver and the transmitter. The receiveris able to parse the MAC PDU from the end in order to quickly processthe MAC CEs if it present.

The transmitter, on the other hand, has more processing time for thecomputation of MAC CEs since they are placed after any MAC SDUs.

Another exemplary embodiment of the disclosure is illustrated in FIG. 30. The drawing shows a PDU format in which the MAC control elements areplaced after any MAC SDU, whereas the MAC subheaders associated with theMAC control elements are placed before any MAC SDU. In particular, theMAC PDU illustrated in the drawing includes two MAC SDUs, SDU1 and SDU2,which are both preceded respectively by their associated subheaders.Furthermore, the MAC PDU includes two MAC control elements, to each ofwhich a respective MAC subheader is associated. However, instead ofbeing placed directly before the associated MAC control elements, theMAC subheaders associated with the MAC control elements are placedbefore the MAC SDUs (all of them within the MAC PDU) at the beginning ofthe MAC PDU. In other words, the MAC SDUs and their associatedsubheaders are preceded by the MAC subheaders associated with the MACcontrol elements, but followed by the respective MAC control elementsthemselves as the MAC CEs are placed after any SDUs and their respectiveheaders and, in this example, also after the padding. In the exampleshown in the drawing, the MAC subheader for MAC CE1 precedes the MACsubheader for CE2, which in return precedes MAC SDU 1, MAC SDU2, and thesubheaders associated with the MAC SDUs. Furthermore, although thesubheader for MAC CE1 precedes the subheader for MAC CE2, the MACcontrol element MAC CE1 follows the MAC control element CE2. This hasthe advantage of an efficient parsing at the receiver. The parsingstarts from the beginning of the MAC PDU and thus, the subheader of afirst MAC CE1 is read. Then, the parser may “chop” (extract) thecorresponding MAC CE1 from the end of the MAC PDU immediately withoutwaiting for further parsing. The parsing continues then with the nextsubheader pertaining to a second MAC CE2. After parting this subheader,the second MAC CE2 can be chopped from the end of the MAC PDU.Similarly, if there are more than two MAC CEs, their subheaders areordered sequentially at the beginning of the MAC PDU while the MAC CEsthemselves are ordered from the end of the MAC PDU backwardly in thesame sequence.

However, the disclosure is not limited to this particular order.Alternatively, The, the MAC subheaders associated with MAC controlelements may be arranged in the same order as the MAC control elementswith which they are associated. Furthermore, the embodiment is notlimited to the MAC SDU including two MAC SDUs and two MAC controlelements; the numbers of MAC SDUs and MAC control elements may bedifferent from two and different from each other. Padding is optionallyincluded in the MAC PDU, if some resources are left in a TB. In thedrawing, the padding is placed between the MAC SDUs and the MAC controlelements, which enables parsing from both sides of the MAC PDU withoutrequiring the knowledge of padding length.

It is noted that the advantage of the present disclosure is provided bythe organization of the MAC PDU. The receiver must be capable of parsingit to obtain the CEs and the SDUs. The way in which the parsing isperformed is not to limit the present disclosure. For instance, even inthe embodiment of FIG. 30 , the receiver may merely parse the MAC PDUfrom the beginning to the end (left to right in the drawings).Nevertheless, additional advantages may be achieved if the receiverutilizes the possibility of parsing the MAC CEs at first and thenparsing the remaining MAC PDU parts (SDUs, padding).

Moreover, the embodiment of FIG. 30 does not require any presenceindicator, since the headers of the MAC CEs are ordered at the beginningof the MAC PDU so that the presence of the MAC CEs is indicated by thepresence of the specific corresponding subheaders.

In other words, according to an embodiment, each second-layer subheaderassociated with any of the at least one second-layer control elementprecedes each second-layer SDU and the respective subheader associatedwith each second-layer SDU. At the same time, advantageously, thesecond-layer control elements are located after any second-layer SDUs.

Thus, a receiver may be provided, of which the second-layer processingunit is configured to parse from the beginning of the second-layer PDU asubheader associated with a second-layer control element and to extractfrom the second-layer PDU said second-layer control element places afterthe second-layer SDU(s).

In the subheaders, the LCIDs indicate whether subheaders belong to MACCEs or MAC SDUs. In a telecommunication system with a PDU structure asshown in FIG. 30 , the receiver parses the MAC PDU from the beginning.If a sub-header belongs to a MAC CE, then the receiver retrieves MAC CEsfrom the end of the MAC PDU, and if a sub-header belongs to a MAC SDUs,then it starts processing of SDUs from beginning.

An advantage this embodiment with regard to the transmitter side is thatthe transmitter has more processing time for the computation of MAC CEssince they are placed after any MAC SDUs. Additionally, available MACSDUs can be already delivered to PHY processing before TB constructionis completed. An advantage with regard to the receiver side is that thereceiver can process the MAC CEs quickly since associated MAC headersare placed at the beginning of TB. MAC subheaders for BSR MAC CEs areadvantageously placed after any MAC SDU, since the existence of a BSR isonly known to the UE after the LCP has been finalized.

As shown in FIG. 30 , the MAC CEs can be located at the end of the MACPDU. However, this is not necessarily the case is a padding CE isinserted into the MAC PDU. According to an embodiment, the second-layerPDU includes a padding buffer status report, BSR, and a second-layersubheader associated with the padding BSR, and the padding BSR and thesecond-layer subheader associated with the padding BSR are placed afterany of the at least one second-layer SDU.

In particular, already in LTE, a so called padding BSR can be insertedinto the MAC PDU. A padding BSR is a BSR which generally does not haveto be included into the MAC PDU since it is not the periodic or thetriggered BSR which is regularly or after triggering to be included intothe MAC PDU. However, if the MAC PDU is assembled and there still is aportion of the resources allocated for this MAC PDU free and largeenough to accommodate a BSR, then a “padding BSR” is inserted into theMAC PDU. Such padding BSR may have a LCID which is different from theLCIDs of non padding LCIDs and in particular may differ, for example,from the LCID values specified for different types of BSRs in Table6.2.1-2 in 3GPP TS 36.321 v 13.3.0. Thus, if a padding BSR is includedinto the MAC PDU, it would be included in FIG. 30 after the MAC CE1,i.e. at the end of the MAC PDU together with its subheader.

Further, disclosed, as shown in FIG. 32 , is a method for transmittingdata over a wireless channel to a data receiving node in a communicationsystem, comprising: receiving 3221 t, from a third layer, at least onesecond-layer service data unit, SDU, to be mapped onto a resourceallocated for data transmission, generating 3222 t a second-layerprotocol data unit, PDU, including said at least one second-layer SDUand at least one second-layer control element, the at least onesecond-layer control element placed after any of the at least onesecond-layer SDU, receiving 3211 t the second-layer PDU generated by thesecond-layer processing and mapping 3212 t the second-layer PDU onto theresource allocated for data transmission.

Additionally, a method for transmitting data over a wireless channel toa data receiving node in a communication system is disclosed whichadditionally comprises determining which type of second-layer controlelement is to be included in the second-layer PDU, and, dependent on thetype of control element to be included, generate either a first-typesecond-layer PDU, or a second-type second-layer PDU. Therein, afirst-type second-layer PDU includes at least one second layer SDU andat least one second layer control element, the at least one second-layercontrol element placed after any of the at least one second-layer SDU,and a second-type PDU includes at least one second layer SDU and atleast one second layer control element, the at least one second-layercontrol element preceding any of the at least one second-layer SDU.

Additionally, a method for transmitting data over a wireless channel toa data receiving node in a communication system is disclosed, in whichthe following steps are repeatedly applied in an alternating order:generating packages that constitute parts of the second-layer PDU, andforwarding packages that constitute parts of the second-layer PDU to thefirst-layer processing unit. Accordingly, packages constituting parts ofthe second-layer PDU are forwarded to the first-layer processing unitbefore the generation of the second-layer PDU is completed. Suchpackages may be respective single SDUs or a plurality of SDUs with theirrespective subheaders and/or respective MAC CEs with their associatedheaders.

Also disclosed, as shown in FIG. 32 , is a method for receiving dataover a wireless channel from a data transmitting node in a communicationsystem, comprising: de-mapping 3211 r at least one second-layer protocoldata unit, PDU, from a resource allocated for data reception, receiving3221 r and parsing 3222 r the second-layer PDU de-mapped by thefirst-layer processing unit, the second-layer PDU including at least onesecond-layer service data unit, SDU, and at least one second-layercontrol element, the at least one second-layer control element followingany of the at least one second-layer SDU.

In an embodiment of the disclosure, the method for receiving dataincludes the step of parsing the second-layer PDU from the beginning ofthe second-layer PDU (i.e. from the earlier received portion to thelater received portion).

In another embodiment, the method for receiving data includes the stepof parsing the second-layer PDU beginning from the end of thesecond-layer PDU until each subheader associated with a second layer CE,and each second-layer CE have been processed, and, after the processingof the second-layer CEs and the respective subheaders associated withsecond-layer CEs, parsing the remaining part of the second-layer PDUfrom the beginning, thereby processing the second-layer SDUs and thesecond-layer control elements associated with the second-layer SDUs. Anadvantage of this method is that second-layer control elements areprocessed more quickly if the second-layer PDU has the formatillustrated in FIGS. 28 and 29 , where the second-layer CEs and thesubheaders associated with the second-layer CEs are placed after any ofthe at least one second-layer SDU, and no padding is placed after thesecond-layer CEs and the subheaders associated with the second-layerCEs.

For example, when the first or any second-layer subheader includes apresence indicator indicating whether the second-layer PDU includes atleast one second-layer control element, the method for receiving datamay include the step of parsing the second-layer PDU starting from theend of the second-layer PDU. An example of such a presence indicator isthe R bit in the MAC subheader associated with the first MAC SDU in theMAC PDU of FIG. 29 . Accordingly, after evaluating this R bit, in thecase of R=1 follows the step of parsing the second-layer PDU from theend of the second-layer PDU, thus evaluating the MAC control elementsand the MAC subheaders associated with MAC control elements.

Alternatively, in an exemplary embodiment, the method for receiving dataincludes the steps of parsing from the beginning of the second-layer PDUa subheader associated with a second-layer control element, andextracting from the second-layer PDU said second-layer control elementplaced after any second-layer SDUs. For example, this method isapplicable for a second-layer PDU that has the format shown in FIG. 30 .The steps of parsing beginning of the second-layer PDU a second-layersubheader associated with a second-layer control element and extracting(“chopping”) the respective second-layer control element may alternateuntil all second-layer control elements have been extracted. Afterwardsmay follow the step of parsing the remaining part of the second-layerPDU from the beginning, thereby parsing at least one second-layer SDUand second-layer subheader or subheaders respectively associated withthe at least one second-layer SDU.

Alternatively, in an exemplary embodiment, a data receiving node forreceiving data over a wireless channel from a data transmitting node ina communication system is disclosed, comprising: first-layer processingcircuitry for de-mapping at least one second-layer protocol data unit,PDU, from a resource allocated for data reception, second layerprocessing circuitry for receiving and parsing the second-layer PDUde-mapped by the first-layer processing circuitry, the second-layer PDUincluding at least one second layer service data unit, SDU, and at leastone second-layer control element, the at least one second-layer controlelement following any of the at least one second-layer SDU.

Alternatively, in an exemplary embodiment, a method is disclosed fortransmitting data over a wireless channel to a data receiving node in acommunication system, comprising: receiving, from a third layer, atleast one second-layer service data unit, SDU, to be mapped onto aresource allocated for data transmission, generating a second-layerprotocol data unit, PDU, including said at least one second-layer SDUand at least one second-layer control element, the at least onesecond-layer control element placed after any of the at least onesecond-layer SDU, receiving the second layer PDU generated by thesecond-layer processing and mapping the second-layer PDU onto theresource allocated for data transmission.

Alternatively, in an exemplary embodiment, a method is disclosed forreceiving data over a wireless channel from a data transmitting node ina communication system, comprising: de-mapping at least one second-layerprotocol data unit, PDU, from a resource allocated for data reception,receiving and parsing the second-layer PDU de-mapped by the first-layerprocessing circuitry, the second-layer PDU including at least onesecond-layer service data unit, SDU, and at least one second-layercontrol element, the at least one second layer control element followingany of the at least one second-layer SDU.

Hardware and Software Implementation of the Present Disclosure

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware and software. In thisconnection a user terminal (mobile terminal) and an eNodeB (basestation) are provided. The user terminal and base station is adapted toperform the methods described herein, including corresponding entitiesto participate appropriately in the methods, such as receiver,transmitter, processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. They may include a data input and output coupled thereto. Thevarious embodiments may also be performed or embodied by a combinationof these devices.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

Summarizing, the present disclosure relates to layer processing at areceiver and a transmitter in a communication system. The layerprocessing includes at least processing on a first, a second and a thirdlayer. At the transmitter side, the third layer receives a packet, addsits header and forwards the packet to the second layer. The second layerperforms segmentation and provides segmented data to the first layer,which maps the segmented data onto physical resources. The segmentationis based on the allocated resources. Retransmissions may take place onthe third layer and thus, the third layer may re-segment the packetaccording to the received feedback for particular segments and providethe re-segmented data to the lower layers. Alternatively, the feedbackinformation is provided to the second layer which then performs thesegmentation by taking it into account. Correspondingly, the receiverperforms re-ordering and re-assembly at the third layer for which itreceives also control information from the second layer.

Moreover, the present disclosure relates to systems and methods fortransmitting data over a wireless channel from a data transmitting nodeto a data receiving node in a communication system. In particular, thedata transmitting node comprises a second-layer processing unit forreceiving, from a third layer, at least one second-layer service dataunit, SDU, to be mapped onto a resource allocated for data transmission,and for generating a second-layer protocol data unit, PDU, includingsaid at least one second-layer SDU and at least one second-layer controlelement, the at least one second-layer control element placed after anyof the at least one second-layer SDU, and a first-layer processing unitfor receiving the second-layer PDU generated by the second-layerprocessing unit and mapping the second-layer PDU onto the resourceallocated for data transmission. The data receiving node comprises afirst-layer processing unit for de-mapping at least one second-layerprotocol data unit, PDU, from a resource allocated for data reception,and a second layer processing unit for receiving and parsing thesecond-layer PDU de-mapped by the first-layer processing unit, thesecond-layer PDU including at least one second-layer service data unit,SDU, and at least one second-layer control element, the at least onesecond-layer control element following any of the at least onesecond-layer SDU.

What is claimed is:
 1. An integrated circuit for controlling acommunication apparatus, the integrated circuit comprising: controlcircuitry, which, in operation, generates a first-type second-layerprotocol data unit (PDU) including at least one second-layer servicedata unit (SDU) and at least one second-layer control element, which isplaced after any of the at least one second-layer SDU; transmissioncircuitry, which, in operation, transmits the first-type second-layerPDU mapped onto a resource allocated for data transmission; andreception circuitry, which, in operation, receives at least onesecond-type second-layer PDU mapped onto a resource allocated for datareception, wherein the second-type second-layer PDU includes at leastone second-layer SDU and at least one second-layer control element,which precedes any of the at least one second-layer SDU, wherein thecontrol circuitry, in operation, parses the second-type second-layer PDUde-mapped from the resource allocated for data reception, wherein thefirst-type second-layer PDU and the second-type second-layer PDU aregenerated dependent on a type of second-layer control element to beincluded in the first-type second-layer PDU or the second-typesecond-layer PDU, and wherein the type of second-layer control elementto be included in the first-type second-layer PDU includes at least apower headroom report, and the type of second-layer control element tobe included in the second-type second-layer PDU includes at least one ofactivation/deactivation commands or a contention resolution message. 2.The integrated circuit according to claim 1, wherein the first-type orsecond-type second-layer PDU further includes: a second-layer subheaderassociated with the at least one second-layer SDU, or a second-layersubheader associated with the at least one second-layer control element.3. The integrated circuit according to claim 2, wherein the at least onesecond-layer SDU is placed after the associated second-layer subheaderand the at least one second-layer control element is placed before theassociated second-layer subheader.
 4. The integrated circuit accordingto claim 3, wherein the second-layer subheader includes a presenceindicator indicating whether the first-type or second-type second-layerPDU includes at least one second-layer control element.
 5. Theintegrated circuit according to claim 2, wherein the second-layersubheader associated with the at least one second-layer control elementprecedes the second-layer SDU and the second-layer subheader associatedwith the second-layer SDU.
 6. The integrated circuit according to claim1, wherein the first-type or second-type second-layer PDU includes apadding buffer status report (BSR) and a second-layer subheaderassociated with the padding BSR, and the padding BSR and thesecond-layer subheader associated with the padding BSR are placed afterany of the at least one second-layer SDU.
 7. The integrated circuitaccording to claim 1, wherein the first-type second-layer PDU includesan uplink second-layer control element, and the second-type second-layerPDU includes a downlink second-layer control element.
 8. The integratedcircuit according to claim 1, wherein the control circuitry, inoperation, starts forwarding packages constituting parts of thefirst-type second-layer PDU to first-layer processing before completingthe generation of the first-type second-layer PDU.